Long time but I thought it best to update. There is an official BMW/Mini repair kit if the roof tie splits. It arrives as a kit of parts for under £30. It will repair both sides. Essentially it is a replacement plastic fixing point part with double sided tape. You trim flush the old fixing point and simply stick it on the old defective part. THen drill three holes and with the rivets and washers provided pop rivet the new part in place. You then reassemble and clip back into place. Tip here is pass some string through the clip when re-fitting. When you drop the clip you can fish it out again. When cliped back just cut the string and pull free. I was quoted £230 / side to do the work. It takes ~20min a side to do.

As I am sure you know Rob, there is no "liability on a car manufacturer" in any shape or form, unless they sold the car direct to the customer- which is extremely unlikely.

The 6 year limit is the time limit for an action in a county court before a claim for breach of contract is time barred..