Some of us here signed on with Warranty Direct. They cover certain performance mods, even superchargers. They're welcomed by Westchester BMW...Manahattan no longer accepts 3rd party warranty and I personally stopped dealing with Life Quality in BK many moons ago.

Westchester had no issues with Warranty Direct and actually told me that they've had a good relationship for some time and receive no hassles (so far).

Manhattan, amongst others, say that 3rd party's are no longer accepted because they've had bad experiences. I think the truth to it is that the 3rd party finds the labor rates of some stealers to be over-inflated and questionable...Manhattan once asked me to pay for nearly 1K worth of work I wanted done, out of pocket, then bill my 3rd party. This completely negates the purpose of why I purchased the warranty...needles to say, I drove off. This amongst many other unfavorable experiences convinced me to also stop going to manhattan.

You may be better off finding a repair shop that specializes in German autos.