Actually, I just finished installing a remote start/ keyless entry system on my 1995 E300 Diesel. I have installed these on W123's and W126's with the OM617's. There are a couple tricks but it isn't that difficult:
Most modern remote starters are diesel capable. This means they have a wire that hooks to the glow plug indicator light OR a built in delay before running the starter. I didn't use the indicator light. I used a 10 second delay instead. This will allow the glow plugs to heat longer and will make cold weather starting easier. (Keep in mind, the dash light doesn't necessarily indicate if the glow plugs are on or off... Just when they have been on long enough to start).
The vacuum shut-off is kinda tricky. These cars have a mechanical valve on the ignition switch. You will see 2 vacuum lines connected. The remote starter will not work unless you retrofit the fuel shutoff. I took a pneumatic solenoid valve off an early 90's Dodge Dynasty (Please don't tell anyone that I have a early 90's Chrysler part on my Benz
. The Dynasty's valve is located in front of the passenger's side strut tower. It has 2-wires and three hoses.
Next I hooked one wire to gnd and the other to the ignition wire (with 2A fuse). Next, I unhooked the vac hoses from the MB ignition switch. The vac supply hose is hooked up to hose barb nearest to the electrical connector on the Dodge's valve. The the other hose (to the injector pump's fuel shut-off) is hooked to the middle hose barb. The last hose barb is left unconnected so it can vent (Don't cap this barb or car will not start).
The operation is simple... applying 12V to the valve (turning the key to ON) will close the connection between hoses. removing 12V from the valve (turning key to OFF) will connect the two hoses. This will apply vacuum to the IP and kill the engine!
Now the car is "electronically" killed. The car will shut off with the key and the remote starter.
P.S. almost all Chrysler cars of that era have these valves. I went a salvage yard and got one for $5.