I've seen the seal, it's a little O ring. My book does have a procedure for replacing, in addition to replacing the entire unit. Either way you will need to adjust the Lambda. My '86 300E was diaged with the very same problem by a the dealer in Seattle. I bought the parts and ended up returning them.
Rough Idle and hesitation, as well as hot start long cranking. My E was not running $1k bad, so I declined the repair and kept driving it. When it finally started raining two weeks ago, the car began running and idling fine and I mean running very nicely! Perplexing. Did the dealer do a false diag? Do I have a vacuum system issue temporarily solved by moisture? Do I have some other seal somewhere temporarily sealed by moisture? We'll see what happens when the weather dries out again. (Hot start is still there, so I now think that is the fuel pump check valve and/or accumulator.)
1986 300E Anthracite + ECodes + MB Mileage Award