I did have a bit of luck. I found out that I didn't need to replace my starter. I had some difficulty trying to get the old one out, but in the process, I cleaned the electrical contacts. Thankfully, that seems to be all it needed. I've been driving the car for over a week with no weirdness at all from the starter.
I also (finally) changed the rear differential fluid. Unfortunately, I damaged the magnetic drain plug in the process and had to revisit the job a week later to install a new drain plug. Luckily, I was able to install the new plug without losing more than a few drops of gear oil.
I also managed to polish the headlights and clean the windshield (in and out) to improve visibility while driving.
NOT MUCH DIFFERENCE, BUT... AFTER
I'm probably forgetting a few items, but I still need to replace the exhaust studs in the cylinder heads (and the manifold gaskets) and the cooling system hoses. Once that's done, the remainder is all cosmetic, and I'll be able to devote my free time to working on the Mercedes again.