Here's what you gotta do.
1) You've got the denial letter. Go thru the stages of grief, and get to acceptance. Beer is cheap in Mexico, if necessary. Also, you are in Cancun.
2) Look at a world map. Find Cancun. Find your house. Examine the distance. Examine the distance to/from the other places you hope to go on this trip. Imagine having a recurrence of this problem anywhere along that route. If you're going further into Central America, BMW dealers are not any easier to find.
3) Look in a mirror. Do you look like a Gringo? Do you sound like a gringo? Remember, you're in Mexico, and when in Mexico, the Mexicans make the rules. Doesn't matter if its fair or not. Remember, politeness rules in Mexico. Mexicans, in general, do not like asshole Gringos. DON'T be an asshole gringo in this deal. If necessary, make up, suck up, buy the shop buys beer or pizza if you have to. Become the anti-gringo. Cancun is full of gringos. I bet the BMW shop has some excellent gringo stories. Don't become one.
4) If you want to be an adventurer, every now and then you will have to pay a stupid / learning / adventure tax. Its happened to me. Suck up and do it right. Do you want (or are you able) to drive all around Cancun looking for a place to resurface your clutch plates so you can save a few bucks? Do you think the shop techs want to do it for some cheap ass gringo who doesn't want to spend money with them? (We are all rich gringos) And what if it can't be resurfaced because its junk anyways? Is easy to do that when you have a shop back home and the abilities and facilities to do a refurbished parts job correctly, and test the results around home. I'd probably try it. But, in the far toe of Mexico, buy the whole darn clutch, the seals, do it right and put it back to together right. In Mexico, parts are expensive, but the labor is cheap. You have a labor intensive job. Doing it the right way, BMW Mexico should then stand behind you if its done wrong. What if you halfass it, get back (or limp back) home (or just as far as Mexico City), then get to pay (possibly with US labor) to fix it all over again- the right way?
Remember, you're in Mexico to have fun and relax. This isn't fun or relaxing right now, but its a man-story for later to tell all your friends how you survived Mexico. This ain't no run to the corner Starbucks. Grab your huevos, empty your wallet, and embrace the adventure that is yours.