Coil stops - When you get a new stern in you need to move the compression washer to the other side of the coil. If you do not move it, it will wedge under the coil stop striker and pop it loose then cause these issues.
Flipper Buttons - Add a 5/16 E clip on the inside of the button shaft on the inside of the plastic lip so the plastic lip doesn't wear out and allow the button to pop out.