Oil leak on to the exhaust. When it's cool crawl under and look for
stains on the exhaust, that's the smoke source.

I'd suggest you wash your engine first... You probably have some oil leak
from valve cover gasket.

The reason you smell those thing is because the seals... two of them
actually... on both firewall by the windshield are bad... so you are
smelling whatever it is in the engine compartment. It is a common problem
with older MB so change those seals and you will be alright.

I would also sugest that you do a thorough degreasing around the
transmission and underside of the vehicle if there is any oil/grease/dirt
buildup.
One of my previous cars (92 Corvette) had a trans fluid leak at the speed
sensor  dripping fluid on the exhaust pipe. Fortunately I was doing some
tuning when the fluid and the accumulated crud cought fire and I was able to
put it out right away resulting only in damage to a wire harness and
connectors..
Ever since that episode I have been paranoid about oil leaks and potential
fire hazards.
Peter