Do the axel seals need to be replaced at a certain amount of used time or time in years. I have a 763 which is 24 yrs old I've owned for five yrs. The seals did not leak and the within a few months two of them started leaking. It has about 2000 hrs on it and I'm replacing bearing and seals since one axel would slide in and out about 1/4 inch. One bearing was needing replaced before long. What I'm asking is if the axel seals need to be replaced ever so often or did I do something to cause this.