96 E300 OM606 won't start at oper. temp. Crankcase position sensor? Fuel pump relay?

[pjc]

Unpleasant experience the other day: Drove 45 minutes, turned car off. Few minutes later, car wouldn't restart. Engine cranked fine (so not a battery or starter motor issue), but wouldn't fire. Sounded like it was getting no fuel. Red and green lights on rear view mirror flashed alternately. I ruled out fuel filters, as they were recently replaced and engine has been running smoothly. No fuel leakage issue in lines, connections, or IP.

Quick phone call to dealer's service department. Service advisor said symptoms are consistent with an overheated crankcase position sensor or fuel pump relay. Suggested letting the engine cool, then try again. Sure enough, after about a 20-minute wait, it fired right up.

Questions for the board:
- Does this diagnosis sound right? Any other possibilities?
- Is there a way to test the crankcase position sensor and the fuel pump relay to narrow/confirm the cause before replacing?
- I thought the fuel pump relay was near the battery, under the back seat. If so, how could it overheat?
- How big of a job is replacing the crankcase position sensor?

Additional info, which may or may not be relevant:
- When I got this car about a year ago, it had the surging problem at highway speed. A thorough cleaning of the resonance and intake manifolds and internal flaps seemed to cure it. It came back last week, but I traced the cause this time to a broken wire on the electrical connector atop the EGR valve. That also threw a code P0400 (EGR flow malfunction), which I had cleared after repairing the wire and before the no-start problem.
- The car also had a persistent CEL associated with code P0380 (Glow plug/heater CKT A malfunction). I replaced all 6 GPs but it continued to throw code P0380. Rechecked GP resistance and found #5 to be higher than the others. Replaced #5 with a new plug verified to be same resistance as others; cleared codes. Voila! CEL stayed off. Until the no-start problem the other day.
- When the no-start occurred, the CEL came back on. I was hoping it would show a code related to the crankcase position sensor or fuel pump relay, but no luck. I read it this morning, and it's code P0380 again. (Now I'm not convinced this CEL was generated by the no-start condition. May be coincidence.) We'll see if it stays off this time.
- The engine itself does not overheat. Operating temp is a steady 85-88 C. Coolant recently replaced (Zerex G-5) with thorough system flush.
- ABS and ETS warning lights occasionally stay on for a while after starting/driving. Seems to be a random occurence and does not seem to generate a CEL or OBD code.
- The no-start problem happened again this morning after my 5-minute ride to Autozone to borrow the OBD tester. So it's not a long-distance issue. Again, engine started fine after a 20-min cooldown.