I recently had my 1979 300SD stolen. I found it after 3 weeks.
They had a key as there were no signs of abuse. Wondering about the complexities and costs of either replacing the locks/ignition or adding some sort of a kill switch. Thanks in advance.

you should be able to remove a full set of tumblers from a 123 sedan, and swap them out. the 126 sedan has the new cool laser cut keys, but that is up to you.
to make it simple, you could go out and buy a wrecked parts car 123 sedan for 100.00 or so and take off all the sundries, but keep the title, so you can get replacement keys from the dealer.
John

__________________
John HAUL AWAY, OR CRUSHED CARS!!! HELP ME keep the cars out of the crusher! A/C Thread
"as I ride with my a/c on... I have fond memories of sweaty oily saturdays and spewing R12 into the air. THANKS for all you do!

My drivers:
1987 190D 2.5Turbo
1987 190D 2.5Turbo
1987 190D 2.5-5SPEED!!!

1987 300TD
1987 300TD
1994GMC 2500 6.5Turbo truck... I had to put the ladder somewhere!

The dealer can also order a new lock set for you.

__________________
1979 240D- 316K miles - VGT Turbo, Intercooler, Stick Shift, Many Other Mods - Daily Driver

1982 300SD - 232K miles - Wife's Daily Driver

1986 560SL - Wife's red speed machine

It would be cumbersome, but you could get a vacuum keeper off of an older GM, and set it up like the locking system, where the shutoff valve always has vacuum applied when the car is not being driven. You would have to put in a open/close release valve so you can drive it. Similar to the manual toggle switch people mount under the dash of an old gasser to disable the coil.

__________________
RRGrassi


70's Southern Pacific #5608 Fairmont A-4 MOW car

13 VW JSW 2.0 TDI 193K, Tuned with DPF and EGR Delete.

91 W124 300D Turbo replaced, Pressure W/G actuator installed. 210K

90 Dodge D250 5.9 Cummins/5 speed. 400K