I did a fair bit of work to the machine and I did have a few plays on it - the ball was binding against the thick aluminum plate that runs next to the kicker (that launches the ball toward the flipper after shooting the ramp) so I tweaked that out just enough to not bind. Not long after, the right hand kicker started staying energized. This of course pops the 2.5Amp slow blow. I'm guessing this binding, i.e., the initial bend because it didn't bind before, and the tweak to correct it are probably a hint as to what went wrong but I don't see it.

I experimented a bit (with a larger fuse in and quickly turning the machine off) and found that I can activate the microswitch (the one above the playfield. The one below tells the computer the ball left?) with no ball in, and sometimes the kicker will work normally (I believe it makes two attempts to clear the ball) ...but intermittently the coil will just stay energized indefinitely. I've looked at the two micro switches in the kicker lane and I don't see anything unusual around them. ...these coils don't have leaf switches.

Good call - left, center, and right trough switches are showing up in the switch test. I had a lot of trouble with weird switch behavior after reinstalling the black plastic ramp assembly... it was an entire group of switches that time (don't recall if it was a row or column) this time it appears to just be these three.

Seems less likely that the transistor would fail intermittently. I'll see if I can find the relay.

Yes - turned out that it was the blue relay under the playfield that had failed. Probably a pretty unusual failure; the relay had a hair trigger, even bumping it would energize it. Signs of some scorching inside.