Rotten eggs smell on 400E

[F.J.Lahme]

I 've done a search on this and found quite a bit of usefull info.
I still have a number of questions though. Perhaps somebody can help me out here.
My 92 400E with 118k miles down is producing this rotten egg like smell, mostly when I punch it a bit harder at an intersection going up a steep hill or after I come home climbing up a mountain side. I don't notice it during in-town-driving on parking lots.but I'm gonna keep an eye, well... nose, on it from now on.
It does not do it after start up at idle or after being at idle for a while or even after reving it up to about 4500 in neutral.
There also is a more or less thick black deposit on the tailpipes and I think the oil smells a bit like gasoline too.
I recently changed the plugs (looked worn but OK in terms of deposits etc), o2 sensor, distr. cap and rotors and yet have to do the fuel filter.
I understand that the 92 400E's are running a bit on the rich side and that the 500E's have a similar issue.
My questions:
Is my problem a problem at all or normal, or something that I definitely should have looked at by a MB tech? My local dealer charges $85/hour and there is really nobody else here on this island who can work on these cars, which is why I normally do everything myself.
Am I damaging the new o2 sensor with this condition or other parts?
Since fuel quality came up as a part of sulfur content causing the smell, is there any brand in particular that can be recommended and lower in sulfur?
Could an older fuel filter cause be related to this?
Also, I will be moving back to California next year and am a bit worried about passing the smog. Is there any real reason to be worried, judging from my description?
The car runs beautifully and is in great condition, beside a few fluid leaks otherwise and I would hate to cause any damage to other parts. Any help is greatly appreciated.
Thanks a lot in advance.
Sincerely,
F.J.