My Sears yard tractor is ill.... Model # 917.257660

Kohler Engine- Model # CV15S Type # PS41508

Seems the magnets have fallen apart on the fly wheel and isn't charging anymore. The part number is 12 025 25. New it's $200.00 bucks. I found a used one for $75.00 the part number ends in an "S" will that work? Am I getting what I'm paying for used? Also I see that most people say replace the strator at the same time? The guy doing the work thinks it is OK.

I know it's 16 years old but it's been a good one! I've had it eleven myself. The engine is strong, the deck & spindles are just a few years old. She's not so pretty anymore but my lawn looks like a golf course. Should I spend the money on it? One more year of school to go... Will the used part be ok for another year of mowing? The guy who is working on it said just buy a second battery and keep a hot battery ready and mow on? What do you think? Thanks for any advice you can offer.