Thanks for the replies.

The leak is not coming from the monovalve, the aux pump, or the metal hose leading to it. It's not coming from anything at the firewall. It seems to be coming from the passenger side of the engine block directly under the turbo. I can't find anything that runs there! Is there another freeze plug other than the one near the block drain that I am missing?

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85 300D 180k

I would think there would be several freeze plugs.

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1976 240D
1976 240D parts car
1970 220D daily driver

So I went in last night and took out things to get access to all the hoses. I used heat resistant RTV around and bypass hose below the t stat to stop a small leak there. I also used a little RTV on the t stat housing as I have now partially threaded one of the screw holes and am also leaking from it. Tightened everything up and let it sit overnight, drove it, and I am still leaking like crazy from the block... it must be freeze plugs.

I think I'm just going to go ahead and add some bars stop leak to stop the bleeding. I don't care if it kills my radiator and heater core at this point, I'm leaking too much to drive the car.

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85 300D 180k