A slight amount of oil on stuff under the intake manifold is not unusual. Make sure it's not getting into connectors and damaging the insulation or preventing good contact.

Glow plugs usually fail open but I suppose they could fail short-circuit (more likely the failure of the insulation allows wires to touch each other). Later pre-glow relays including 1995 contain a self-resetting circuit breaker rather than a fuse. I have never had an opportunity to observe this phenomenon.

I have a light added to my instrument cluster that illuminates whenever the #1 glow plug is energized. It stays on during afterglow and then goes out. This enables me to confirm afterglow and detect a stuck-on relay or a relay that fails to energize.

If the relay detects a failed-open glow plug, it still energizes the others but it does not turn on the glow plug light in the instrument cluster.

I have not conducted the test done by dieselbenz1 so I cannot comment on a reduction of voltage during afterglow; must measure that sometime.

Jeremy

__________________

"Buster" in the '95

Our all-Diesel family
1996 E300D (W210) . .338,000 miles Wife's car
2005 E320 CDI . . 113,000 miles My car
Santa Rosa population 176,762 (2022)
Total. . . . . . . . . . . . 627,762
"Oh lord won't you buy me a Mercedes Benz."
-- Janis Joplin, October 1, 1970