MB190 whats under right side fender?
 

Looking up at two plastic balls?W201

It's a reservac. It's evacuated during engine operation and maintains a constant supply of vacuum for vacuum operated engine controls.

Ok thanks for reply, couldnt find it in the vacuum diagram drawing. Very little info about this, what are you searching for on internet?

Half a century behind the wrench:

http://www.coolcatcorp.com/190Restoration/Mercedes23.jpg

Yes the reservoir is on the other side on the 89mod, charcoal canister laying horizontal on this side and made of plastic, no worries about rust! Check the bondo covering weldings inside there, they look okey but often lose and when there is a hole it start rust underneath. Best just remove it and do some threatment before sealing up with paint and oil so you have control of it.