1 quart a month isn't much depending on how much it was driven. Make sure you're using the proper weight oil I know a lot of euro cars take high viscosity oil.
Also the tail pipe being 'greasy' can mean a couple things, I'd recommend going to a different shop to have it looked at. Without seeing itI can think of a couple things that can make it 'greasy'. Hell if you're running rich it'll get a black suit that gets slimey when even the slightest bit wet, for all we know that's the problem. A good mechanic should be able to know more by seeing it in person, but frankly there isn't a definite answer that we can give you over the internet.
Can't think of any problems that would be an 'ohh my god sell it now' situation. It's not like a rod tap or a cracked head. If it's running fine that kinda rules out rings and head gasket as that would through of compression or cause a 'dead' cylinder, but as I said diagnosis over the internet is hard to begin with. Take it somewhere else though. It seems like they see someone with a BMW and want to bend you over the parts counter, considering they gave no indication of what the problem could be.
We have a couple bimmer fans here that'll hopefully weigh in as I'm not too familiar with 'em.