This happened to me a while back and quite quickly once it started acting up. Your days are severely numbered...a small plastic part in the shifter assembly appears to be your shift lever misbehavior.

Over at the other forum is a well documented how to to fix:

[benzworld.org/forums/w220-s-class/1455706-shifter-stuck-park-handy-tools-heres.html]. Additional threads add tips such as how to do it without going under the car. Just search "shifter" or "shift lever".

It looks complicated but if I could do it, most anybody can.

Note also but not mentioned in the how to - mine also had a small plastic nut on a plastic stud sticking out of the front of the shifter module that you can't see. You'll find it by feel -IIRC, it is an 8mm nut.

This is an astonishingly expensive repair at the dealer (they won't fix the shifter - they require a whole new shifter assembly and coding/programming to your vehicle) Well worth the 3 or 4 hours of your time.

You also have to decide if you want to delete that broken piece without replacing it - you lose that lock out safety freature. You can source a new lever to replace the broken plastic one. It is metal and I believe someone over in Australia offers them (surprise - a couple hundred bucks if I recall but a new shifter from MB approaches $2K!)

If I am correct in believing this is your shifter problem, you don't have long before you're immobilized...

Good luck,
Kevin

__________________
"Dangerous with a wrench...and not smart enough to know it"

Stable (in order of acqusition):
'84 500SL, 280SEL (Euros)
'77 280SE. '90 560SEL
'79 450SEL 6.9,
'95 C280 (totalled by daughter 8/07)
'81 280SL (rescued) '88 300CE
'86 560SEC '95 C36
'01 CL55

DD's: '04 S500 4Matic (SWMBO)
'04 F150 Crew