Look for the source of the leak in the front of the engine as well as the rear. Specifically the water pump and associated fittings.

This may sound far fetched but it actually happened with my '89 wagon a few years ago. Your tranny mount replacement is what prompts me to tell the story.

I had a water pump that was starting to go. I hadn't noticed because the coolant was finding it's way to the splash guard and being contained there. But after raising the front of the car to do some work underneath (clutch replacement, actually) I found coolant in the place you describe; at the bottom of the apron behind the sump pan. I also remember finding a drop or two on the left side of the engine below the cylinder head. Apparently it had migrated after raising the car. I can think of no other explanation since, after tracing it to the front (that's when I finally noticed coolant in the splash guard) and replacing the pump, I have had no more coolant loss.

Obviously, you want to rule out the stuff that's easy to check before going to the trouble of inspecting the [your descriptive preference here] plugs.
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'80 DL 2 door, '89 DL Wagon