I have a very similar problem with my 1988 190D. I personally never touched the lines, as I'm waiting for a manual. However, it does leak on occasion, esp. after my alternator died and I let the car sit a day or two until I got the new one on. The leaking has completely stopped since, for now. It did leak on occasion before, enough to leave silver dollar-sized stain on the driveway overnight. At other times, the leak seems to be gone. It doesn't seem to matter if I have a full tank or near-empty, but I plan to pay closer attention.
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I know nothing about this car's history, except that it wasn't taken care of very well. It had pet stains all on the carpeting that I had to yank out and sanitize. The nice oversized chrome rims have a few dings on them, and there is a buffed-over swipe on the passenger rear quarter panel, with stress fractures on the tail light housing. We joke that this car must've been a getaway vehicle at some point. There are miles of monster cable and screw holes from prior amplifiers and speaker boxes in the trunk. Grandma did not own this car.