Help: Rotten Exhaust Odor

["Roger B. Hui" <rbhui@xxxxxxxxxxxxxxxxxxxxxxx>]

I have an E34 1994 530i, with a persistant rotten exhaust smell.  The 
engine (3.0V8) had new block (BMW covered) a few months ago, and the
smell started right after.  The dealer (Patrick of Schaumburg, IL)
claimed the odor comes from the brand of gas used.  I've tried different
brands since (Mobil, Shell, Amoco) with no noticable improvement.

Any suggestion are appreciated.

PS.  There is also exhaust gasoline fume from under the hood after the 
engine work.  I am suspecting that the exhaust manifold/gasket is loose.  
Could these be related?

PPS.  The reason the engine block was replaced was "premature wear" 
from dealer.  I was never given the cause, but found some suggestions 
(via net) that it was due to the sulfur contents of American gas.  
Anybody experienced this?

TIA.
Roger

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