Not that this solves your current issues, but make sure to order yourself a clear playfield plastics protector set from PinBits for when you clean and reassemble the topside.
http://www.pinbits.com/index.php?main_page=product_info&cPath=13_88&products_id=625
It will protect the plastics you have left, and at least keep the ball from getting hung up where you're missing original plastics.