o-ring size for 12AX7 & AT7 dampers?

How hot do these tubes get? Silicon will only take so much.... Other elastomers can take more heat. EP, for example....
'snug' is good, apparently.
I have DowCorning Silicon StopCock grease, a white/clear grease used to lubricate O-rings.....VERY sparingly. In the industry I worked, the philosophy was to 'put none on and take it all off'....THAT sparingly.

I've been using McMaster-Carr's part number 116 S70, silcone o-rings, as dampers, for the past 12 years. No need to add anything(grease, etc). They handle the heat of the tubes, without any ill effect, at all. I've had the same rings, on and off, numerous times. Matter of fact; I've still got a number left in the original bag. E-mail me, and I'll send you a few.

UPDATE on the McMaster-Carr part number. It's now AS568A-116. Like I said: I got mine 12 years ago. What I posted was the number off the bag they came in, then. (http://www.mcmaster.com)