Getting oil on it will kill them faster than anything. How does it look? Is it weather checked or oil soaked? Is the outer ring still in line with the inner? Can you put some force against it with a prybar and get excessive movement? I've only heard of replacing them when they fail or while one is already off. May also open a can of worms trying to replace it as preventative maintanence too.
Just somethings to think about,
Scott
