Was fine then one day just noticed it was weak. I have not had a chance to check it out yet but thanks for the replies.
I had a weak left flipper issue that haunted me for a little while when I had STTNG. It would play fine for days/weeks and suddenly just go very weak. I had checked:
1) All the mechanical parts (listed above in my previous post)
2) EOS switch working and gapped properly
3) Voltages to the coil, power driver board, fliptronic board
4) Engaged the coil by manually grounding transistor from the fliptronic board in the head and at the actual coil
5) Swapped the cabinet flipper boards from left side to right to see if weak flipper would move over to other side
6) Check the actual flipper coil tabs to make sure there isn't a break in the small coil winding to each tab or poor/cold solder joint
I was out of ideas and since the weak flipper would come and go the last thing I suspected was maybe the LM339 chip was bad on the fliptronic board.
I picked up a bunch of LM339 chips and sockets from Sayal and removed the board to drop off to Menace. I figure since he was removing the chip might as well get him to help me install sockets in case this happens again in the future so I could easily remove the old chip and pop in a new one.
When I had the board out I noticed one of the fuses had a little bit of burn inside the glass tube so I pulled it out to test with my meter for continuity. It tested just fine and I didn't think to test any of the fuses as all my flippers appeared to be working and getting the proper voltage. The problem ended up being a lower spec fused (2.5A) was used for the lower left flipper which was just good enough so the coil would get power and flip but not blow. I popped in the proper rated fuse from the manual which was 3A and voila fixed!
I know the previous owner of the game had experienced the same weak left flipper problem when he owned it. He thought he fixed it by replacing with a new brand new coil. Anyways, hope your problem is a simple fix like this one and make sure you check all these things before you start throwing new parts at your game or doing unnecessary board work which could cause collateral damage
Worse case you can always call Menace for a house call to address your weak flipper and any issues you might have with your other games since his first hourly rate factors in travel expenses. Also you never mentioned if you have one weak flipper or both on your IJ.