I'd head back to the place that did the oil change for me right after the timing job. Odds are that they have records to show that the work was done. I know that the quick-lube place I used to go to for my wife's car would send me a post-card every 6 months after I had the work done saying "hey... it might be time for another oil-change... here is a $5 coupon if you come back to us." I've had some great experiences with MINI dealerships, but I've also seen some places slide over to the dark side... a change in ownership, management or reporting practices (you get results based on what you measure and how you compensate employees) can push behavior in the wrong direction (which may have happened here). The service department at the dealership where I bought my MINI in 2005 went that way and lost my trust. The dealership that I swore 'never again!' turned things around and really became a shining star (IMHO) on how to treat customers. I'm betting that this poster was PO'd (deservedly so, if his/her story is accurate) and wanted to tell his story to the world. I'd like to hear how the story unfolds.
The car and the issue exist. I feel the dealership bashing was unwarranted based on the information I've uncovered. MAG will do the right thing because that's the way Sammy works. One of the best service managers I've ever dealt with. I truly wish the OP the best in getting this resolved