Thanks. Sorry for the delayed response, but I've been using this post as a guide to go through things a bit more: https://pinside.com/pinball/forum/topic/sttng-f104-fuse-keeps-blowing/page/2#post-2268964. This has been pretty strange; I've fixed things like this before, but this one is not quite like the others.
A quick recap: the coil was locking on in test. Note: it only locked on after being activated - it did not lock on as soon as the game was powered on. I did some basic testing, pulled the PDB and replaced all 3 transistors for the coil, along with the 74LS374. Put the board back in, reconnected everything, and the coil still was locking on. Then, without me even touching the game, the problem mysteriously disappeared the following day and the coil worked normally. And then, about a day later, the problem came back, again without me doing anything (I'm working on other things).
I visually inspected the wiring on the coil and tested other coils to see if there were any other new issues. At that point I found that none of the high powered coils worked: sure enough, fuse had blown. I replaced the fuse and booted the game again. As soon as I closed the coin door, the fuse blew again. That is what led me to the post I mentioned above.
I ran through the various suggestions in that post, pulling the appropriate connectors, checking for grounding at the pins, etc. and didn't find any issues. I pulled the PDB again and re-tested ALL transistors for ALL the high powered coils, including the associated diodes this time, and everything was good. Put the board back in, powered the game up, and surprise: the coil was working as it should.
One thing I realized I did wrong during the above is that after pulling the board the first time, when I put it back in I wired it up, but I did not screw it in, so it was just "hanging" on the mounting screws. Since those screws provide grounding, is it possible that the original problem actually was the transistor/74ls374, but then everything that happened after that was due to the board not being secured? Or that the coil itself is going bad? I feel like I'm grasping at straws, but considering all the other tests made things appear to be OK. I bought this game as a project, and I really want to get it out of the house now but I don't want to list it for sale without being reasonably sure this issue has really been fixed. Any insights from someone more experienced with diagnosing these kind of problems would be greatly appreciated.