I have an FM that I got a few years ago at a swap meet. The camera/meter kept draining the battery even with the thumb thing in the off position. I spent more than the camera cost me to try to fix it. Then the flash synch went out of synch and again I had it fixed for more than I originally paid. Then the little screw on top of the advance lever, the one about a half inch round and covered in leather, fell off in an airport somewhere. Keep an eye on yours. It is a nice little camera but not worth getting fixed.
Dennis