I've read numerous threads on similar issues, took action accordingly, but the problem is still there.

My W126 300SEL used to stall intermittently, just cut off suddenly and wouldn't start again. Solution was to wiggle the OVP relay a bit (along with the wiring below), until it starts back up. In the meantime, I had some work done on the car, and among other things, new crankshaft position sensor (original from MB), and new spark plugs have been installed. The cap, rotor and HT leads were inspected and seemed OK.

Now, a different issue presents itself. The car starts (and it seems to me that it runs smoother than before), runs fine for an indefinite amount of time, and then just stalls when idling. Earlier, when I attempted to restart it, engine cranked but there were no signs of life. Now, engine starts up immediately, runs for about 1-2 seconds, and dies. I tried to get it to high RPM and see if it'll stay running, it revs, but dies anyway. This all happens when car is at operating temperature.

I changed the OVP relay this morning, car ran fine, but as I was pulling in to work, it died again. I tried the old trick (wiggling the OVP), and it started, but died when I tried to drive it, and would start only for 1-2 seconds at a time (as explained above). I wiggled it again, engine started and kept running long enough for me to get it into parking space.

Right now it seems to me that the wiring below the OVP might be at fault (loses contact, so wiggling solves it shortly), but I haven't found anyone who experienced such an issue.

Edit: Another thing - my ASD light used to be on all the time (It was like that ever since I bought the car), but just prior to the first stalling it went off and never turned back on. I don't know if this is related.

I believe that the fuel pump relay is mounted next to the OVP relay. Could wiggling the OVP be moving the FPR as well. They are a common source of intermittents due to cracked solder joints. The FPR can be bypassed to confirm.
I think the car should run without the OVP but possibly someone can confirm that.
What year is your car?

In W126 ASD relay is next to OVP. My car is 1989, Euro-spec (for Swiss market). I don't think moving the OVP moved it as well, as I detached it from the mount bracket.

However, I might be on to something. I started the car today, and while it ran, I moved the OVP relay around in order to see whether the engine will stall, but nothing happened. Then I started looking at the rest of the wiring and noticed that the diagnostic port located on the left fender is loose, as well as the two wires connected to it by phillips-head screw. Sure enough, as soon as I started fiddling with those, engine started to rev up and down, then died. I left the ignition on and moved them some more, and I noticed that one of the relays (OVP or one of adjacent ones) started clicking, and fuel pump turned on and off. I cleaned the contacts and tightened the screws (1 phillips-head and two 10mm), and the car's running fine. I haven't driven it much though (just home from work), as I'm afraid it'll stall on me again, but I'll go out late tonight when there's less traffic and see what happens.