Hi John,
I had exactly the same issue with a 1966 230 SL USA model. The car was imported into Ireland in 2008 ( no issue was raised then ) and then into Portugal in 2016... Then the problems started . The motor vehicle registration authorities stated the VIN didn't match the title "end of story". For over a year I tried...tried logical arguments, took photos of pages from w113 books that explain how these cars VIn numbers etc are made up, got the Mercedes Benz subsidiary and MB classic center to write a letter stating that the vin and title corresponded and that 230SL at the end in the title was never part of the original title but a substitute for the w113 in the start of the vin , photos of vin /tags etc .... No result ... I managed to track the issue back to the last USA title I could find. Exchanged emails with California/USA and was told to send the car back to the USA with the title and the local authorities would check and validate if correct !!!!! I almost despaired and was about to break up a pretty decent car.
Then I decided to call the Motor vehicle authorities ( not sure of the correct name ) , explained the issue and then sent over the current Irish title with the "incorrect "VIn the MB letter, the photocopies from the specialist books etc.... A week later I received a new Irish title with a matching corrected VIN.
Problem solved , car registered and new title issued in Portugal. The original title had an additional problem which you don't have .. The last number in the title before the 230SL was a J instead of a 5, a mistake likely originated from handwritten registration many years ago where a handwritten 5 could be confused with a J. This was also sorted with the same MB letter etc in Ireland.
All it took was one understanding lady bothering to listen and look at a few papers to understand these issues. Hopefully you will find someone who will do the same.
Good luck.
Cheers
Pedro