how to value Fisher preamp


I have a Fisher 400-cx-2 in the walnut case, 100% original, never touched and is 100% working condition. It is part of my dad's system that he assembled in the early sixties. He was always very fussy about it and and it shows. He passed many years ago, and mom feels like it is time to sell it off, but we need to get some ides about price and if anything needs to be serviced. There is also a Fisher KM-60 tuner in the walnut cab that works perfectly, stereo beam and all.
Two of the knob trim covers (gold)are off(one missing), but the knobs are still intact. I am wondering about finding the knob cover and if they can be re-glued?
Do vintage pieces like this need to be re-tubed, or if working well just put up for sale, and how does that affect value? Any input is helpful.
rtiff
If you are looking for more than $10 at a garage sale, then these units should definitely be serviced before being put up for sale. The service person should have a good idea of the value of the piece.
That's just my opinion. I know I would not shell out what some folks will pay for vintage units without some form of service documentation. I might take a flyer on something at a yard sale w/o documentation, but if you think it's worth more money, it will be up to you to provide the proof.
This always seems a strange question. The inevitable answer is, it's worth what someone is prepared to pay for it, at the time. That is the advantage of an auction, whether on this site or E-bay. Providing you give a longish period to generate interest and there are at least 2 interested parties, it should find the best price at that time.

A lot of the problems with "expert valuation", is that the expert is'nt buying the item. The price will vary, it depends how many are on the look out for the item at any one time.
Leave them in completely stock condition. Do not attempt any repairs or mods. The value of the units depends upon them being stock and in excellent cosmetic condition. The brass knob inserts are not important, but discoloration of the front panel metal is. The preamp is far more valuable, you could get $1,300 - 2,000. There is one on ebay right now for $2,500. I think it is over priced, but you should follow the sale. The tuner is worth $150 - 300.