I had a similar leak on my 380 SE. Turned out to be the hose going to the steering column. You couldn't see the leak but evidently the braize was broken at the flange to the reservoir. It was tough to remove at the column end. Use 2 wrenches. One to hold and one to turn the fitting off. No more leak but the hose was 90 bucks at FastLane.
Mike
84 Euro 500SL
85 380 SE