Thanks for the input. There are always people with problems, but this doesn't seem like the normal small bunch of complainers that always exist. The very fact that "Plenty of people on here and dpreview had their circuit boards replaced by Canon..." shows a hardware problem exists that is a lot more common than a typical (rare) manufacturing defect would be. It's great if you get a good one, and not so great if you don't. And, we don't know if these issues show up right away or appear with time and use.
The only time I ignored a similar volume of online user complaints was regarding an AF problem on the 1D Mk III and 1Ds Mk III, because lots of users seemed extremely happy with it. I bought the 1Ds Mark III for $7800, tested it, and found no problem. Later that year I got a bunch of randomly mis-focused photos on the other side of the world that I could never photograph again. By then Canon was replacing mirror boxes free, even out of warranty, for anyone who found the problem. After repair it was an excellent camera that I used for many years, but I'd never voluntarily go through that hassle and loss of images again.
I'm in no hurry and I'm still on the fence about buying an R5, especially with the R3 supposedly coming out soon. If it's around 50MP it could be ideal. Sony's A1 isn't going anywhere either, except perhaps to a lower price as all of this unfolds. This could be the ideal time to use what I've got a little longer.