Images: 1, 2, 3, 4, 5

The leak got a lot worse pretty suddenly - so it’s now leaking something like a few gallons an hour I’d guess (Though water is the one utility we don’t pay for here, so it’s annoying but not world-endingly urgent). So I decided it was time to get around to this - but when I got to the point in the images, which is right after the escutcheon you mentioned, I was no longer certain how to proceed.

Based on the images, is this still a relatively simple job that I can do with one or two trips to Home Depot? I don’t really know what I’m looking at here - would I grab the hex bit the white part is sticking out of and start turning with a large wrench? If so, the rest of your advice is still relevant - take the seals to Home Depot and look for as close a match as I can, since I looked and looked and couldn’t find a manufacturer’s name?

As of right now I’ve re-assembled it and turned the water back on. I did get a look at the pipes at least and they seem to be copper. There’s drywall behind the pipes that I would absolutely be willing to let a plumber tear into to avoid tile work. If I did end up calling a plumber, and nothing went wrong, do you happen to know the general ballpark of what it may cost?

Also, sorry. I know I’m asking for a lot of information and advice here. If you’re not up for another round of free advice I’d totally get it.