95 s500 exhaust smells sulphur

[ramco18]

I am a frequent visitor of this great site and I thank all of you for your time and dedication to discuss MB cars.

I have this problem with my car, 1995 s500 (mileage 37400) where the exhaust smoke occassionaly smells like sulphur.
I use Sunoco Super or Shell Super gasoline.

Dealer has changed the following:
Catalytic converter
Air flow valve/sensor
Engine timing parts
One injector
o2 sensor
Remaining 7 injectors.

All above done around 27,000 miles. After above replacements Car had no problem for about six months. Now the problem seems to reoccuring. Is this a known problem on 1995 s500's?

Dealer has been very co-operative(starmark car), but its a nuisance to take the car back so often, it takes them one day to diagnose, order the part and install on third day!!!!!!

Any suggestion about the cause/remedy will be helpful.
I thank you for your valuable contribution

Ramco18