My '88 420SEL is VERY slowly leaking power steering fluid, it starts to groan when I turn the wheels every two or three months or so. My mechanic installed a kit to stop the leaking, but I almost doubt that he did anything, because the problem's come back.

Anyway, my question is, is the a serious problem, or should I just keep adding fluid as needed? And, how do I know how much fluid there should be? I don't see any markings on the inside of the resevior (I don't really know what to call it). I bought MB power steering fluid, I just need to know how much to add. Thanks alot for any help.