Have you tried taking it to another Peugeot dealer (not owned by the same group)
Mb aren’t bothered if the garage can’t fix it, they would prefer to be rid and sell it on and get a decent price for it, as used car prices are still high. The problem for you is the AP’s are still higher than 2yrs ago and dependng on the car you may have to wait far longer to get.
This is imo one of the few area’s the scheme still shines – you can just swap it with little to no questions asked. Imagine if you were a retail customer you would be stuck with it unless you could afford another or running yourself ragged tring to get it sorted.
I would clarify with Mb should you decide to terminate your lease you get any pro rata AP back, good condition bonus/payment and there’s no termination fee.