Quick update: After bathing the clip latch in rubbing alcohol and drying it the performance improved a tiny bit. It was chopping fresh paint consistently and I had to tug on the clip a bit after the first shot to get it to keep going. Technically this is an improvement.
After working on I am worried it is just old. My dream of eliminating someone in a game with an SMG-60/68 seems doomed now. Will keep trying but I have no realistic expectation of having it to go in time for the end of the month game. However, I do want this to be working at some point if possible, so if anyone knows anything about these or has any advice on the matter please advise.
Thanks.