***General rant to follow, not directed at the original post*** :nerd:
A quick way to scare off any free repairs is to have an entitled attitude, even if the entitled attitude is justified. The reason why is that MB / dealers are SOOO used to folks giving them project vehicles that were tampered with, and most, if not all states have laws that require Work Authorizations to be signed.
Once these "$0" Work Authorizations are signed, the dealer is on the hook for vehicle work and things can snowball from there. What if the dealer tech has the vehicle up on a lift and realizes that a prior shop had disconnected everything and put things back together sloppily, literally causing the needed repair issue? What if, there are bolts or screws that are cross threaded or electrical wires have been spliced into?
If the car is say, 5 years old and 70k miles on the road, an owner may feel entitled to a free fuel pump after having an expectation of a longer interval between fuel pumps. Nothing wrong with that expectation. However on the flip side, accepting responsibility for the free repair work also means accepting responsibility for anything and everything else that can potentially go wrong down the line. Up to and including vehicle damage, scratched paint, damaged interior, technician injury, lawsuits, etc, etc, not to mention it is quite conceivable that the owner sabotaged the car with 80 octane fuel. An extreme example, yes, but it definitely happens.
There are just a certain percentage of folks who will manipulate and lie about the vehicle history prior to bringing it in for free work. That's why having an attitude, even if it may be justified, any attitude is not going to work in your favor if your vehicle is out of warranty. Presenting yourself like an agreeable, likeable, trustworthy client, is the best way to go. A history at a local dealership may be a good way to demonstrate that.