The '95 E300D indeed has a monovalve, Sixto, the one that leaks. The twin exits from the heater core join together at the base of the valve, which has a single electric plunger. The valve is special in that it never shuts off the flow of coolant but rather directs it either through or around the heater core. IMHO, this is purely for smog reasons—a constant flow of coolant through the head makes head temperature easier to control. It also means the valve/pump combo is unique to the '95 E300D, except for a very few, very late 300D2.5 OM602 turbodiesel engines. Thus the extreme price, now well over $500.

Jeremy

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"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