I had a similar thing happen with some rubber footings I had beneath a center channel speaker. It's a good reminder to everyone to move their equipment every once in a while so that it doesn't happen again.
My system was in my 14x25 medium room in my basement. So the temp is not hot or to cold . The transformer coil was on spikes . The main part of the preamp just sat on the rack. I think it all depends on the the product used by the manufacture . I have other pieces of equipment of same vintage and no problems with the feet.
" I think it all depends on the the product used by the manufacture ."
It must. I have a 40+ year old Pioneer SX-980 that has been dragged around several states and various climates and the feet look fine but are somewhat dried out and lost their elasticity. Easy enough to replace.
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