Audio Research installs tube dampers on its products from the factory, and that should tell you something. I've never had a damper melt, just get brittle, and I could always tell by ear when they hardened and needed to be replaced. The classic test is to tap one of your input tubes with the eraser end of a pencil while your system is on - if you can hear the ringing through your speakers (which will always be the case in my experience), put a damper on it.
