W116 280SE stalls when hot and restarts when cool. Why?

[stevefzr]

Hi Folks,
My daughter has a W116 280SE from 1976. I had it for a few days recently while I did some work on it and it ran great, however I didn't drive it in peak hour traffic. She's having problems when she drives during peak hour. It seems to happen every couple of days. The car stalls when hot and won't restart for 10 or 20 minutes. It's not getting hot enough to boil. The car seems to be in a good state of tune. I recently put in a new coil, did plugs, points etc and it made no difference.

I suspect that it's a heat soak problem, where heat is eventually affecting one of the electronic components, like the fuel injection computer.

A couple of years ago the car used to start running badly and then fix itself. The problem was traced to a faulty fuel injection computer and it had a reco unit fitted. It also had the fuel injection points (I've no idea what these are) replaced because of intermittent poor running. Neither of these issues caused it to stall completely and not restart.
Because this only happens every couple of days, and my daughter doesn't live at home, it's going to be I possible for me to wait for it to fail and then try to diagnose the fault before it fixes itself. As she's normally alone in the car, I even doubt I can get her to crank the car and check for a spark the next time it happens, especially as it usually leaves her stuck in busy traffic.

Is this a common problem, and if so, what are the usual causes? I guess it's either losing spark, the fuel injection is stopping or it's suddenly running massively rich. She's a bit of a girly-girl, so I can't expect her to pull a plug when it happens and check if it's wet or massively carboned up :-)
I may be forced to just keep swapping components until the problem goes away, but I'm reluctant to do that as the fuel injection computer and FI points were both expensive items to replace. I can do any work required, I just need some tips on where to start. I guess if I could find a working FI computer for $50 instead of the $300 I paid for the reco unit I wouldn't mind doing a swap.
Regards,
Steve C