The problem is that because they are rubber (Hence made from an oil product) that once they get old and have oil on them (For long periods) they start to break down.So there strength goes out the window.Now we are talking just mm it needs to hold and so on.So as the rubber gets weaker it can't do the job.I've found that in many mowers to be the problem.Glad I could help.

Here for a good time,not a long time.