Working my way through a list of niggles and issues on my 1994 Cabriolet (a new acquisition this year).
One thing that is rather annoying, in 2018 M-B of Greenwich (ie a main dealer) replaced a few items for the original owner, one of them being the trunk lock cylinder. Apparently it was not working, and on the service invoice it says "Original part no longer available from Mercedes-Benz, ordered 124-750-15-91 lock cylinder with key as service part as approved repair by Mercedes. This will not function with alarm but trunk will lock and unlock with central locking".
This is indeed true. Trunk locks and unlocks with the vacuum locking system just fine However, when I got the car, the elderly prior owner lost the new key that fit the trunk cylinder . After a look, we've given up on it surfacing so now I need a physical trunk key.
I still have the original 2 master and 1 valet key for the car, but none of these 3 keys of course fit this new trunk lock cylinder. I'm worried if the power lock fails I'll get locked out of the trunk so I do want a key.
So -- should I:
1) Just buy another 124-750-15-91 w/ a new key and call it a day and install that? (possible without key?)
or
2) I've never had luck w/ locksmiths really cutting keys to lock cylinders, so starting over with another #1 seems a better option if I can do that)
or
3) Could I either buy a new 124-750-15-91 cylinder and have it re"coded" to my master keys (that would be ideal) Or recode my current "no key" cylinder to the rest of the keys?
Also, small addendum of my question. The alarm on this car for whatever reason will not arm and the alarm dash LED never blinks. I've swapped ECU's with known good and checked wiring. Could this trunk lock cylinder be the reason? All locks etc work normally with exception of the passenger side which will unlock but not lock the doors. I think the microswitch is bad.
Thank you in advance for any experience or advice on above.
Congratulations on your '94 C124 Coupe.. Join the club!
I went through this NLA MB cylinder lock nonsense back in 2016 .... I'll pull the service receipt doc's later tonight with the possibility of shedding some light. Gotta Zoom ...
OK, so I've gotten the lock latch out, with the trunk lock cylinder in it. You'll remember I'm missing the key for this trunk cylinder.
Is there any way to remove this cylinder from the latch without the key ? (which is missing).... and just buy a new MB spare part cylinder that comes w/ a new key? Or do I need to buy a lock cylinder AND the latch thing it fits into? I do see that the latch wasn't replaced as it still has 1994 date code.
Pics here
I'm trying to get this trunk lock cylinder out of the trunk latch (but don't have the key) 1994 date code on trunk latch. Still works perfectly. Ugh corrosion. Luckily caught it in time. Not rusted at all on the underside of the metal here, so ... yeah. Fixing that up -- grinding down, painting with rust paint (Eastwood or POR type, will topcoat with midnight blue sprayed on to look decent -- all covered by the black plastic trunk interior trim panel so not visible...)
BTW for future searchers. I figured it out. The key cylinder (and the black plastic around it) simply slides out of the bigger latch assembly with a little help from a screwdriver.
Basically just like this document which is from a W140, but by looking at this, I realized it's the exact same methodology to remove the W124 coupe / convert trunk cylinder assay from the latch.
. After a look, we've given up on it surfacing so now I need a physical trunk key. 
