I saw the 'set' on the rubber dampers long ago (after about 150 total hours) and started checking it at intervals from 100 to 300 hours.   The set did not change significantly so in my opinion the dampers only need to be replaced if the rubber material itself is starting to deteriorate.  Mine haven't after 1200+ hours.   The set will be noticeable after very few hours so replacing them at that point would get old in a hurry.

I was concerned about some change of properties of the elastomer; like ‘hardening’ with age and heat. Checking them further, they seem OK. I’m thinking I’ll rotate them 180 like the A&Ps do with the engine mount elastomers on the certified craft. Make sense?

Al