300E bad / worn bearing noise ?

Hi

I have a 1987 300E.

I can hear a noise that sounds like a bad bearing in the housing behind
the 
distributor cap.

I took a large long screwdriver and placed the tip on the metal housing
that 
the distributor attaches to.  Just behind the top center of the cap, think

the 12 O'clock position.  I pressed my ear into the handle end of the 
screwdriver and I can hear it loud and clear.

I haven't had a chance to look at the manual as I have the manual on cds.

What bearing would this be and what is involved in changing it?

Thanks