This seems to be the most common explanation for spontaneous restarts. Same happened to my TAF. The voltage is certainly another possibility, but much less common than the BR.

I don't really have the skills to repair this myself so I looked into repairing the board. After the quotes I got (and the lack of warm and fuzzy I got from the guy I spoke to) I decided to replace he entire board with a new (modern) one from Rottendog. Probably would have spent the same on repairs.

Nope. But I will look him up in future
I went to a local gameroom shop and Stern distributor (who shall remain nameless). Their repair department said they would need to spend some time "diagnosing" the board at some ridiculous hourly rate in order to determine what was wrong, even though I was pretty certain where the issue was.
I still have the old board and a friend of mine employs a really good tech that has done repairs for me in the past. I just hate to ask for too many favours. One day I'll take it up there and have him do it for me... or I'll get up the courage to attempt it myself.

I totally agree, but I also have to trust the person I'm paying, and the guys I referenced (like some mechanics) don't necessarily have the best reputation for price/service. I didn't want to come out and start slandering anyone so I left it at that.
For me, TAF was my first pin, my knowledge was zero and the cost and promise of a new and improved board on my prized TAF was an easy decision. Knowing I would always have the original as back-up made it an even easier one.
Maybe one day I'll have enough confidence, knowledge and skill to accurately troubleshoot and attempt to fix some of these more technical issues. But as you implied, a little knowledge can be a dangerous thing.
Luckily, the quick fix worked for me that time... your mileage may vary.