Engine Mount Bushings ... short life

This is a problem any one can have. AGE of them, who know how long they have been in someone stockroom. There was someone in the early 2000 who said they had a new formula for them that made them last longer.

I replaced all my engine mount bushings about 18 months ago (on a C-85) and now I find they are cracked and deteriorated.  I purchased the bushings from Spruce (Continental Engine Mount Bushing Part Number: SA22387).

Any advice on where to find higher quality bushings (or an approved alternate)?

For reference I'm based in Wisconsin and the airplane is always in a heated hangar.