Given that it was 1365 yesterday and 1367 today, that suggests that the problem isn't an individual glow plug, but somewhere in common circuitry.

Absolutely no difference in ability to cold start (I did have the block heater plugged in this morning, but needed only the same small amount of cranking to fire this morning as last week).

Also, I reset the code this morning while driving, and the code set itself again before I got to work (there was no engine restart in between setting the code twice).

Without knowing more about the circuitry (yet), this suggests it's not an actual glow plug failure, but perhaps a glow plug staying on?

__________________
Mark in MA
05 MB E320CDI 402k Granite Grey Metallic
05 MB E320CDI 267k Black
05 MB E320CDI 232k White
05 MB E320CDI 209k Tectite Grey
99 Dodge 2500 Cummins 5sp 148k
62 Jeep CJ-6 120k