I replaced my ignition lock cylinder using the $20 ebay tool. I used this HOW-TO guide to do so.
https://www.500eboard.com/forums/showthread.php?t=4718
In my typical ham fisted fashion, I took 1.5 hours to accomplish what should have taken 15 minutes.
Firstly it took me a ton of time to figure out where in the key's rotation I should be sticking the tool in. I kept on rotating the key to position 1, and having the dashboard lights light up, only to find that the tool would not sink in the holes. Even after jiggling the key 1mm or so in either direction an endless # of times, that didn't seem to help.
Finally I rotated the key back a little bit to the point where the dash lights shut off --- BINGO -- that's when the tool sunk in.
Gerry should be relieved that my keychain is an MB one - not a Porsche one.

The pictures below show the position that I had to use to sink in the tool:
My old lock cylinder was not broken and looked to me fine --- I will consider this replacement then to be a preventative measure -- and I get an extra key out of it! Pictures of the old ignition cylinder below:
My second mistake was in trying to re-install the whole shebang together --- the plastic trim, the rubber boot, the steel sleeve, and the ignition cylinder. Stuff wasn't lining up and all, and the ignition cylinder just didn't want to go in.
So then I tried installing the individual pieces in. I fit the ignition cylinder in just fine, and the key turned. YES.
Then I tried installing the ignition cylinder AND the metal sleeve -- without realizing that the metal sleeve needed to click in place. I pulled the extractor tool out of the little holes and then realized that the the key wouldn't budge. MINI PANIC until I put the extractor tool back in and pulled the whole assembly out again.
Then I was playing with just the metal sleeve (no ignition cylinder) --- and realized that the metal sleeve needed to click in place --- and click in place it did, without having the ignition cylinder in there! MINI PANIC again until I followed Allgonquin's advice in using the extractor tool to pull the sleeve off again. WHEW.
Now, understanding how everything fit together, I installed the ignition cylinder AND the sleeve together ... made sure that the key turned, and then I installed the plastic trim and rubber boot.
All done. Satisfying. No swear words used. I consider that to be a success.
