MBWorld.org Forums - Diagnosis for my newly acquired 2000 C230 Kompressor

Hello, everybody! First time posting here and also a first time Mercedes owner. I'm hoping you all can help me diagnose a problem I'm having with my 2000 C230 Kompressor.

It's a no crank no start that is a bit intermittent, getting worse lately. Typically it's been a hot start issue, it would start up cold, but would take a couple extra turns to get going. It never sounded weak or anything like that. If all I did was take it one place (work) let it sit for a while and drive it home, it was fine. But, if I took it anywhere else to do errands or anything in between, there was a good chance it wouldn't start up again. I turn the key and nothing happens, no cranking or even clicking. Typically, I'd need to let it sit overnight or even longer, then I'd try it again, and it would start up fine, like nothing ever happened.

This last time, though, I took it to work and after sitting for 12 hours, it wouldn't start up. A couple of days later, a friend was going that way, and was able to start it and get it home, though he said that the starter sounded weak this time and barely fired up after turning over multiple times.

Here's what I've done to diagnose so far:
-I had O'Reillys hook up their battery tester to the battery. They also did a starter power draw test, and tested the alternator. The machine said everything was fine. (The battery was a couple weeks old, so no surprise there)
-I asked a friend from work to hook up his diagnostic machine, but it was showing no codes.
-I bought a multimeter and tested the battery myself. It showed my battery's voltage at 12.3, which was a little concerning, because as far as I know, minimum voltage is supposed to be 12.4v (is that correct?). I charged the battery with a battery charger pack, the voltage read 12.9v, but after about an hour, it dropped back to 12.3v. Is this enough voltage to engage the starter?
-I pulled and inspected every fuse, with everything seeming to be in order.
-I tested the relays by supplying power to them from my battery, and putting my multimeter on the other two prongs of the relay switches, and everything was good, except one, but as far as I can tell from googling that's the relay for my windshield washer pump.

https://cimg3.ibsrv.net/gimg/www.mbw...9b102a6395.jpg Fuse that wasn't working (it was literally rattling) I didn't even bother testing it.
-My next task is to borrow a torx socket from a friend, and pull/bench test my starter.

Anybody else have this problem? This is the first car I've ever worked on myself, and have been googling/youtubing my pants off to learn as much as I can to try to fix it myself because, of course, money is tight these days. Any help you guys have would be greatly appreciated.

Thanks in advance!