Your almost better off going to a small time shop versus a Rover dealer. Theres a guy in town who owns this little cinderblock shop, been there for years. I happen to know him, and I asked him idly one day if he could do the work when I eventually have my transmission rebuilt. He whipped out a catalog, and turned to the ZF section.
Shift kits, parts, gaskets, valves, gears, bare housings, you name it. Guy says, sure, I can do it.
There is a speed shop in a barn outside of town where the guys know both the Rover V8 and the ZF transmission like the backs of their hands. I mean really rebuilding and fixing things, not just replacing everything.
Also, an independant BMW service center can realy help you out with the transmission.
I don't go to chain shop mechanics. They all suck. The guy you want fixing your car is the one who made a life decision to cover himself in grease every day, not the guy who just couldn't get another job.
ZF also has a list of authorized service facilities on their website, and they are all over the place.
Cheers,
Kennith