Also check these sites:
http://www.mercedes-benz.ca/index.cfm?id=6872
The following is a quote from UCANIMPORT.COM:
Saturday, July 5, 2008
Mercedes-Benz Imports Exempt From Letter of Admissibility
RIV List Updated To Show Admissible List of Mercedes-Benz Models
We are pleased to report that as of today importers of Mercedes-Benz vehicles from the US will not require to apply for a Letter of Admissibility. The RIV list has been updated to show which Mercedes-Benz models are admissible to Canada.
Importers may obtain admissibility information from www.riv.ca or from Mercedes-Benz Canada at the following web address: www.mercedes-benz.ca/admissibility
A separate Letter of Admissibility is not required from the manufacturer's head office.
Previously, the requirement for a Letter of Admissibility made it difficult for importers to negotiate on vehicle purchases in the US as they required advance written confirmation from Mercedes-Benz Canada that the vehicle in question would be allowed to enter Canada. In addition, the Canada Border Services Agency (CBSA) would request proof of admissibility prior to allowing the vehicle to be imported into Canada.
Waiving this requirement means importers simply have to verify the admissibility list before completing their negotiations and purchase in the US.
Posted by UCANIMPORT PUBLICATIONS at 9:12 PM 9 comments 
Labels: Admissibility, Mercedes Benz
Do the research cause the rules changed frequently in 2008 and early 2009. Anything more than 15 doesn't need much, so that would explain the ease of importing an 86 in 2006.
Going to be interesting to see what happens with the inadmissible 1995 MB cars in 2010. Supposedly they will be 15 and mean that they are admissible, but are still listed as inadmissible. When looking for 95 wagon I contacted RIV in regard to this and got a very confused answer so I went out and bout a 97 SL instead.
Good luck and please post your results with the importation process. In a lot of ways I have found that the results vary from location to location. Also noted some inconsistencies in who has to do the modifications to bring the car in to compliance with federal legislation.
jb