Tinker:
If you show a leak on the rear of the compressor, it's likely your speed sensor (attached to rear) or one of your case section O-rings is leaking. (red lines in pic below) It appears you have a Nippondenso 10P15C compressor on your 190E.
I recently rebuilt my Nippondenso compressor and it was surprisingly easy with the help of
this article. Tightening down the 5 section bolts as Larry mentioned might do the trick too.
My leak was coming from the middle section O-ring. The only 'special' tools you'll need are a pair of snap ring pliers (for the circlips) and a strap wrench or large channel locks to hold the clutch while removing the front bolt. Autozone also lends out a compressor clutch holding tool.
You can purchase the gasket kit from
www.acsource.com
Good Luck
