Thumbs up for ultrasonic record cleaning

@gbanderhoos-you raise some interesting points, starting with the actual operating frequency of your KL. I wonder how much variability there is among units in the field?
We are told that 40Khz doesn’t cause damage, at least for relatively short duration at fairly high rotational speeds (AD, KL); most of the DIY set ups seem to rotate at a lower speed, and for longer cleaning times, no? (I have only owned the AD and KL, but am aiming for a DIY when the KL goes, mainly for operational flexibility rather than low cost). I prefer point nozzle vac drying to forced air or passive air drying since I think it does a better job of removing the vestiges of contamination and fluid. I learned pretty quickly that the commercial US machines intended for LP did not clean challenged records that could get clean using AIVS No. 15, some vigorous agitation, pure water rinse, sometimes repeating the process, and then employing the US, with a final rinse and vacuum using high purity water.
I pre-clean any used record (and a few new ones that are obvious dirty) before going into the ultrasonic, using a Monks, and high purity rinse. I only find a deposit of very fine grit in the KL tank from new records that have not been pre-cleaned.
As for damage, I suppose you could test using a blank LP, examine for pitting, etc.-a point raised by a vendor of new cleaning service who opted for 80khz transducers run at low power (Perfect Vinyl Forever, who has recently been posting about his equipment and methods on various fora).
I’ve certainly heard no evidence of damage, which would be one good way to discern--most revealing to me are the results I get from a record cleaned both by conventional (fluid/vacuum/rinse/vacuum) and US, sometimes repeated conventional cleanings using AIVS No. 15 and reagent grade 1 rinse--where the record initially exhibits low level noise, raspiness, tracing distortion-often associated with groove damaged records. These can in many cases, not all, clean up to be quiet players. Once I clean a record using combined methods and it plays well, I don’t re-clean or do follow up re-cleans.
I’ve also had records that I cleaned decades ago using a VPI and who knows what fluid at the time (I tried several including some home brews) that play beautifully today.
I’ve also been reliably informed that using a surfactant in the US enhances the cavitation effect dramatically. Perhaps using a surfactant reduces the need for lower frequency, higher power and reduces the potential risk of damage, I don’t know. I found the earlier AD to be kludgey in operation, the KL of course doesn’t permit the use of additives as far as I know, thus my aim for a DIY which permits use of a surfactant.

@whart - Thanks for your thoughtful response. The general consensus seems to be that US RCMs do not cause any damage; I suspect that if any microscopic changes (damage) are occurring, it is subtle, random, isolated and cumulative, possibly evading detection via listening tests for several cycles.

I also suspect that given the number of variables, the amount of cleansing action (and by extension, over cleaning and possible damage) varies greatly with each application. I doubt that damage would be heard as an average degradation across the entire LP, but would be random and very limited until it became severe enough. My thought process is to better understand the mechanics of US cleaning in order to optimize the cleaning process while minimizing the potential for damage. My impression after reading this thread (and others) is that few people using these devices fully understand what is occurring and are relying on mfrs specs and hoping for the best. My impression of the electronics driving the KLAudio transducers is that of a very simplistic approach, adjusting one important parameter (frequency) in order to obtain a desired specification (power) without fully optimizing the process.

Some of the industrial tanks vary the frequency and therefore the power to create "waves" of transmitted energy to improve the cleaning process. While the average power may be 150W, the peak power could be many times higher. The KLAudio machine maintains constant frequency, but the DC supply to the output transistors is essentially unfiltered rectified line voltage so the transducers "pulse" at 100/120Hz with peak power ~280W.

FYI, I use both IPA and surfactant (tergitol) in my KLAudio RCM for the past 2 years. I know it voids the warranty, but so far, I have not experienced any bad side effects.  I also vacuum the records after cleaning with an Okki Noki.

@whart Thank you very much for your informative input! This is similar to the process I'm currently using, but I do not rinse after the vac pre-wash since I US clean with the same solution as I vac (5% IPA + 0.05% Tergitol).
What do you use for your US cycle? Just high purity water?

@bydlo - i have not added any surfactant/detergent to the water since I’ve been using the KL. When I got it, I was using Reagent Grade 1, which seemed to be a waste of money. Now I just use distilled in the US, but for a finish rinse on valuable or challenged records, I’ll use the Reagent Grade 1 and vacuum on the Monks. As mentioned, when the KL goes, my plan is to try a DIY approach, largely b/c of the feature set, which includes the ability to use a surfactant to enhance cavitation effect.
For now, I just change out the bath water every thirty records, even though most of them have been precleaned. (Yeah, I’m a little compulsive, but I don’t have a filtering system hooked up to the KL).
Not to open a can of worms- I think this was discussed earlier in this thread- but the idea of alcohol and ultrasonic makes me a little nervous. I gather most of you are using only a small amount. Since I haven’t mixed any chemistry for ultrasonic, I can’t contribute to a meaningful discussion about what alcohol adds. I know in the old days, using vacuum, alcohol was commonly part of the cleaning fluid. I don’t think it is a terribly good solvent. Perhaps it is the evaporative properties. (I’m not concerned about damage to the vinyl since I think the exposure to the plastic is limited, but the flash point does concern me). Maybe I’m a nervous nelly.
There have been some good suggestions here on different chemistry. I use an lab grade detergent to clean my lab dishware which can be used in an ultrasonic machine. It isn’t very expensive. 1 part per 100 or 200 is recommended. It foams like crazy when I am hand washing the various glass I use hold brushes, and mix one of my RCM fluids (Hannl concentrate, which I dilute with the reagent water).  
I think there's a little Walter White in all of us. :)

@whart That's what I thought - KL discourages use of any add-ons no? Honestly, I'm sticking with alcohol just by some inertia. I like it for its grease dissolving properties. Also as far as I understand, it actually makes the 40kHz cavitation gentler by lowering  water's surface tension. Having said that, next tank solution I'm gonna try will be just water + 0.05% Tergitrol, excactly as used by the Congress Library and see if I get less clicks n pops. I also tried pure water US but I'm a bit afraid it may be too aggressive
plus I like the Tergitol solvent properties.