[MBZ] Oil leak in front of engine

[MICHAEL ESH]

1973 Mercedes 220D.  
Problem; Oil appears to be leaking at a very slow rate (uses about a quart and 1/2 between changes) from the bolt that holds the alternator tension adjuster to the block.  The bolt is  tight as it will go and there is about a 3/8" play between the block the adjuster and the bolt.  
The adjuster moves back and forth from the front to the back on the bolt.  
Is something missing on the bolt/adjuster assembly that would cause this leak?  

I noticed leak after the AC Compressor and mount were removed.

Thanks in advance,
Mike