what color is your PS fluid?
If it is red, get it out of there because it is most likely ATF.
Change the fluid to any PS fluid at least, but you may want to try one with "seal conditions" .... can't hurt at this point. You could also change the filter although I don't think it is a direct contributor to the pump leaking.
If the above doesn't work, check around for quality rebuilt units. You give them your core. I have had good luck with these, as long as you get one that is correct for you car and rebuilt properly.
Also check with this site's part department. They are great and very helpful.
'03 E320 Wagon-Sold
'95 E320 Wagon-Went to Ex
'93 190E 2.6-Wrecked
'91 300E-Went to Ex
'65 911 Coupe (#302580)