15.5 no spark issue time after time.

I have a 2000 craftsman mower with a 15.5 Kohler engine. The issue is after it sits for a few months I get no spark, no start. every time I cleaned the rust off the flywheel magnets and replaced the coil. It runs fine. I'm on my third coil and again no spark. The last time it seemed the flywheel/magneto magnets were very weak, Do these go bad and lose their power? Sometimes it mat sit for 7-8 months and that's when it seems to act up.

15.5 no spark issue time after time.