1. Please post pictures of the inside lower part where the handle connects. It might be in the "piston" (or air pump) of the handle that's causing it to stick. Usually you can remove that part and clean it.
2. Your payout slides are probably gummed up, or you have a broken spring - so one is stuck open, resulting in a payout each time. People sometimes oil them and they should NEVER have oil.
I'm a novice at mechanical slots but I can give it a try until someone else chimes in.
Post the handle lower part picture as well as the bottom of the payout tube, where the slides are.