I have a 1986 190E that failed smog a couple years ago. My former shop de-carbonized the engine and it passed. The car is not a burner to begin with so I was surprised it failed. Depending on where you're located you could check with Barooni Imports and ask for George in Mountain View. Or, you could call Marshall at Silver Star in Oakland (510.834.1090). He's a dismantler and service shop who's been at these cars for 30 years. Another place in Oakland is AllMercedes at allmercedes.com. But, Marshall could tell you whether or not you got forked and probably what to do about it.

EDIT:
Barooni Imports Auto Sales
1905 Old Middlefield Way
Mountain View, CA 94043
(650) 969-4400
http://www.barooni.com


Marshall at
Silver Star Motors
1727 17th Street
Oakland, CA 94607
phone: (510) 834-1090


All Mercedes
1225 7th Street
Oakland, CA 94607
Monday-Friday: 8:00 am - 5:30 pm
Saturday & Sunday: CLOSED
Tel: 510.763.8602
Fax: 510.444.2345
http://www.allmercedes.com