I have a irregular but increasing in frequency starting problem...the original key fob has been replaced recently, and it has not remotely unlocked since I rec'd it from the dealer...I live very very far from a MB dealer, and am blessed with a really excellent mechanic who has kept my little fleet running well for over a dozen years...he could not program the key fob, and has gone over it many times with MB and cannot get it to work...the key works fine as far as unlocking and starting...the other original keys (non fob)
work fine...but with every key, the car occasionally will turn over (as if the kill switch is triggered), but after a couple of attempts, the car will fire just fine, and may not do it again for a week...the idiot lights do not come on either, so I can instantly tell that it will not fire on this crank...so after a couple of turns the lights come on and all is well...when I am having this starting problem the green and red flashing do NOT flash as they do when you have an alarm issue or kill switch...I am not technical at all, and will relay your suggestions to my mechanic..the closest MB dealer does not enjoy a wonderful service reputation either...very unlike the one that is 150 miles away. Appreciate any and all input.

 

I've seen a lot of early 210 chassis with bad ignition switches, it sounds like thats what's wrong with yours.
As for syncing the key I think you just operate the ignition and within 30 seconds you get out and aim at the IR reciever and push the button,