New starter in a 172 2005

I'm being told that I'll need a new starter and ring gear in my plane
(used intermittantly by a school). The last one didn't seem to last
very long... It was flooded by an instructor and cranked it "a bit
longer than usual" to get it started. The mech. startes this as the
reason they failed.

Just how long should a starter and ring gear last under normal
conditions? The last one cost about $380.00 (I'll have to check and
see the make/model on the paperwork).

Did my mechanic cheap out just to save a few dollars? Should I be sure
a top-of-the-line model is replaced or push for a warranty replacement?