The drive pin (or torque pin) is not available separately as a new part from MB.
(Photo of the drive pin is by step 10 on the third page of the
W126 pdf, FSM page 1683)
It is sold as a unit with the door handle ($$$).
It is detachable from the door handle, so you can replace a damaged one with a good used one from a junkyard W126.
Unfortunately if the tumbler ever goes bad, you will need a new keyed door handle from the dealer.
The tumbler is not designed to be replaced as it has a inaccessible blind rollpin holding it in place.
The tumbler is not available as a separate unit, but one mght be able to drill out the blind rollpin to allow extraction of the tumbler from its housing.
I was going to attempt this, if the seized tumbler in 'Rena 2.0' didn't free up with cleaning and lubing.
Good luck with your DIY repair, the FSM is your friend.
