So, took the whole family in the car to a big event today. Well, tried to.
Stopped at the gas station to top off the tank. First pump didn't work, went to go to the next, both E85 pumps have someone getting regular gas, just parked, not at their cars. Annoying. They finally move, I go put a few gallons in the car, go to start it... no start. Put my jump pack on and it fired right up. Fine, not a big deal, it'll have time to charge up on the way out. Went to put the car in 1st and it "clunked" in a bit, weird. Felt like the shifter wasn't quite right; remember this has an S1 Sequential on it. Start moving and the car dies. Ok then. Fired right back up, idled down and seemed fine, back in first, another clunk, shift linkage feels a little weird, but car ran fine. On to the meet-up before the show.
This is a big event for the driving club I'm in, and we parked 160+ cars prepping to go to the big festival event. I pulled in, car seemed fine, so I parked in my assigned spot, and we walked around for a bit. Get back in the car and checked the shifter.... no reverse. The S1 has a secondary lever you push forward to get reverse and it won't go forward AT ALL. Zero movement. It also still doesn't feel right for forward gears. I yanked on the reverse lever and boom, I have forward gears but no reverse. Great. The cruise to the event goes right by my house, so I figured I'd split off from the pack and try and fix it quick.
Got home and, yeah, not going to be quick. 30 minutes later I had the console and shifter out and I could see the issue. The reverse lockout/enable lever connects to a little triangle on the shifter assembly on the transmission, which it rocks back and forth (think over-centering lock) to put you in or out of the reverse gate on the transmission. Instead of rocking back and forth it had kicked around 180* and was inverted from where it should be. Well no wonder it felt weird and wasn't shifting right. I don't know what turning that 180* does in the sequential assembly, but apparently it makes it mad.
So, I hit it with a hammer, as one does. Sounds bad, but it was just to knock it back into it's proper track, at which point the shifter felt normal. Cool, so it's fixed, but I don't want it do to that again.
Solution! I drilled and tapped a hole for a 1/4-20 bolt and a locking nut, then ground an button head bolt to be a positive stop for the reverse selector lever (the other direction can't over-rotate so only one positive stop is needed).
Shifter assembly:

Reverse gate selected:

Forward gates selected:

Didn't get to go park with the club since it took me the better part of an hour and a half to tear the car apart, fix the first problem, and re-engineer the system to prevent it happening again. We just took the Tesla to the show as spectators since the Mustang was determined to be a dick tonight.
Oh well, at least I fixed the problem I didn't know I had.