I would guess that your leak is the output seal on the pump itself, just a shot in the dark, the reservoir is very simple and I can't picture anywhere it would leak except for where the hoses connect. A quick look will most likely tell.
My advice would be to clean up the whole area, jack it up, get right under using every safety precaution needed to not get hurt. Wipe down everything, especially right where it looks like it's leaking now if you can see it. you pretty much can spend as much time as you want, there are a lot of shiny gizmos down there that always need cleaning. Then drive the car around, now not in the rain, it must be dry. Your leak will appear somewhere, maybe just some new hoses and clamps. Don't forget to order a new power steering oil filter and change the fluid while your at it. Might as well get the gasket for the reservoir lid. The leak could be a very small intake leak on the suction side and possibly foaming your oil, look close at all the connections, that leak isn't as visible as a pressure side leak. And never ever run your hand along a hydraulic hose while it has pressure, it can inject fluid into your body and cause infections.
My car had the groan, checked everything out, oil level stayed full, and no leaks. My bleeder screw is broke off in the power steering gearbox. So I just jacked the car up with it running did the lock to lock thing a bunch of times and it went away. Now whenever I jack it up I do that while it's up there.
The whole pump, if it is the pump is around $200.00, I still can't imagine the reservoir leaking, but who knows with the W113, it has it's own set of rules.