I am generally hugely negative on extended warranties in almost all contexts. BUT, those provided by the OEM are a rare exception. The reason 3rd party warranties make little sense is that they are a zero-sum game--if you win they lose. And, if they were losing on average, they would not be in business. OEM warranties are different. There are two reasons for this: (1) they can fix your vehicle for less money than anybody else (because they own all the spare parts and they have the dealers under their thumb); and (2) they have a vested interest in keeping you "in the family." For these reasons, it is at least within the realm of possibility that a manufacturer's extended warranty might make sense. Whether it ACTUALLY makes sense is a quantitate question that is difficult to answer. In the case of the Sprinter, I am inclined to think that they ARE worth considering, if you are fairly sure that you will continue to own the vehicle for the duration of the extended warranty period.
A couple of things to note, though:
--Even if the warranty is transferrable, I doubt that a future buyer is likely to reimburse you for your investment, so if you are NOT likely to keep the vehicle, it is probably not worth it.
--You can purchase a MB extended warranty at any time before the basic warranty expires. It makes little sense to purchase it before then. Yes, the price may be a bit higher, but you will have kept your money until then, and you will know the vehicle and your relationship to it much better by then.
--For dealers, extended warranties are high markup items. For this reason, they are prime targets for negotiation. I like to save them for the point in the negotiation in which I am "ready to walk" (meaning I have squeezed as much as possible from the dealer). As I walk out the door, I turn around and say "OK, tell you what. Sell me an extended warranty at your cost and we have a deal." It often works. You will be surprised what their actual cost is. (This, of course, is an exception to the "don't buy it now" rule).