The magdyno platform wearing is very common as no one ever checks if the strap is tight. They put the magdyno on the bike and tighten the bolt and never ever check it again.

Before every time you ride your M20, put a spanner on the bolt and make sure it is tight!

I once saw an M20 with the magdyno literally dancing around on its platform to the point I was surprised the gears were meshing. The unconcerned pilot kicked it into gear & chuffed off.