Just going to reinforce what it seems others have learned here. My SDTM issue from the trap door was being caused by play between the armature and the coil sleeves. I replaced the coil sleeves and armatures with Marco parts, also the springs. Everything works great now, except I believe the newer Armature Extension (04-10019) from Marco may be about 3mm too long, or the screw hole attaching the trap door lid to the armature may be a couple mm off. This results in the trap door lid not sitting flush on the playfield. You can either replace the original armature, or bend the bottom stop bracket (with the rubber grommet) a couple mm until flush.