If yours is anything like my E300D W210, the pump and reservoir are one piece, attached to the engine. There should also be a quite noticable pully there, driven by the accessory belt.

The power steering fluid lines attach to the control valve on the rack. This valve sounds like where you see the leak. I haven't taken the lines off of mine, but they appear to be attached with banjo bolts (those large bolts that you mention). I'd check those fittings for leaks first.

If it is leaking at one of those fittings, the stop-leak probably won't have any effect.