I purchased a MINI BASE CARRIER, part number 51 95 2 354 325 and it did not require any modifications to fit.
Car is a 2004 facelift saloon, were all head restraint spacings the same?
I wonder if different makes have different spacing on the head restraints?
I will now order another one for the other side - hopefully by using the same part number I will get an identical base to the one just received.