Got the job done, only took me 4 or so hours with my ADD. Not bad - a brake job takes me longer, lol.
The junkyard unit had some corrosion on the aluminum casting, and some of the connections seemed a little iffy. Upon pulling the switch out of my steering column, it was in visually better shape, so I was worried that my replacement wasn't going to work but I went through with it. Turn signals both work, high beams and even flash-to-pass now work. Really relieved that I've finally done this after 3 years this month of owning this car and the issue getting steadily worse.
Some issues I came across during the replacement:
The countersunk 10MM screw holding the steering wheel on was a pain - if I had a friend it would've been easy to hold it still and turn the breaker bar, however I managed to get my foot on it and steady the wheel enough to break it loose. An impact probably would've done it too but I don't have air in my garage.
The two electrical connector retainers in the multifunction switch for the clockspring had me confused for quite a while until I realized I had to pry two tabs down instead of one to slide them through.
A lot of screws were missing in the lower instrument panel, it's apparent that it's been removed before. It was a pain getting the instrument panel back in place because gravity really didn't want to let it go while I was trying to start the screws in it, but after some wiggling I could hold my knee against the bolsters to hold it in place.
I was going to make a writeup on it because there's very little said on here about replacing the multifunction switch as far as time, cost, other potential parts needed, but I found a thorough writeup for the R170 SLK that was exactly the same for our non-SRT cars apart from us not having a screw in the driver side air nozzle vent, which you pry out around the edges with a plastic wedge tool instead. That write-up, with photos can be found here:
Mercedes-Benz SLK 230 Turn Signal Stalk and Combination Switch Replacement | 1998-2004 | Pelican Parts DIY Maintenance Article
Multifunction switch Mercedes-Benz part #170 540 03 44