Easy to take apart even with monovalve still in car. Drain a couple of quarts from radiator until you see expansion tank empty, to recent spills. Disconnect electrical plug. Remove 4 screws (Torx) around metal solenoid of monovalve. Note position of pieces (photos are good to help reassemble). Lift up solenoid and all connected pieces. Examine for damage or other source of your problem. Should take only a half hour.

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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