Quoted from Reznnate:
Q1. It crashes mid-game and then fails to reboot with a black screen and '99' in the bottom right corner of the display.
OK, I missed this the first time I skimmed through your post. I've seen this before. You have something shorting on the motherboard.
When we first saw this years ago, it was caused by the screw holding one of the feet on the bottom of the metal chassis. (The big metal box that holds all the electronics.) The screw was too long (or perhaps over-tightened) and it would touch the bottom of the motherboard.
My suggestion is to remove the motherboard from the chassis and look underneath it. (Shake it upside down while you're at it, just to make sure there isn't a loose screw or something sitting on it.) Assuming that a foot screw is a problem, you'll need to insulate it in some way. Several layers of electrical tape should do it. If I'm not mistaken, later games were shipped with a piece of "fish paper" under the motherboard. You may want to contact Support to see about getting a new one if yours is missing or damaged.