After spending most of the spring enjoying the results of my hard work on the 300D, I've decided I need a new project or two ... so I'm trying to resurrect the 78 240D, again. It starts fine and drives fine, but the idle is pretty dreadful and there's a heck of a lot leaking, including fuel I can see running down the front of the injection pump. I can't see any on top of the pump, but my guess is delivery valve seals, because I can't figure how fuel would get on that part of the pump from anywhere else (or I suppose it could be the line leaking). Since the seal rings are cheap, would that be a reasonable place to start? Or am I missing something obvious?
If I do the delivery valve seals, am I correct in concluding from searches that there is only a copper washer involved, and not the rubber seal that's in some other engine's pumps?

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1987 300D, arctic white/palomino--314,000 miles
1978 240D 4-speed, Euro Delivery, light ivory/bamboo--370,000 miles
2005 Jeep Liberty CRD Limited, light khaki/slate--140,000 miles
2018 Chevy Cruze diesel, 6-speed manual, satin steel metallic/kalahari--19,000 miles
1982 Peugeot 505 diesel, 4-speed manual, blue/blue, 130,000 miles
1995 S320, black/parchment--34,000 miles (Dad's car)