77' 450c eats starters

[Sabaro]

Our 450c has had the starter rebuild 3-4 times in the last 10 years. The tractor is no longer an every day worker. Gets use maybe a maybe 15-20 days a year. we always cover it with a tarp in the winter. The Generator/Starter repair shop we have been taking it to said its getting water/moisture in it which causes rust. we just had it rebuilt last year and It broke down shortly after repairing it, so it cant have more than 20hr on a rebuilt starter and just last week it stop cranking. Same symptoms as always. Is anyone else having starter troubles? I feel that a starter should last longer than what we are getting out of one. Could we be getting poor rebuild job, and should I just buy a new? Thanks Sabaro

[Lavoy]

That seems quite excessive to me. I would look at new or a rebuilt with a warranty the next time.
Lavoy

[Sabaro]

Have you ever heard of condensation causing problems, or is there a chance the engine block could leaking into the bell housing where the starter is?

[Lavoy]

I know I have had starters apart with some rust in them, but getting hot and cold would have to contribute to that somewhat. Plenty of these engines get steam cleaned, you would think that would put moisture in there, but don't hear about many problems with that.
Lavoy