I'm sincerely sorry you've had so many issues. I come from the same boat with my 2012 451. However, one big issue in reporting to the NHTSA hopeful for a recall are that the car(s) in question are almost 10 years old now. These issues aren't the same as say, a Takata airbag exploding shrapnel into one's face.
My 2008 Pure had a seat-belt problem a couple years ago, seat-belt buckle would not seat & latch. Visually obvious. The Florida Smart dealership insisted that a $300 diagnostic must be performed prior to any consideration of the problem & remedy.
That's normal, they have to figure out why that seatbelt wasn't working. Even if you had the now standard 4yr/50k warranty it would still have been out of warranty.
Now one leaks fuel out from a hole in the plastic pan, which many of you have already experienced. Don't yet know if it's a G&K modified gas tank fitting crack failure, or fitting sealant failure that I sometimes read about here. What years were affected by G&K fuel tank modifications? Or maybe it's a fuel pump failure? Or something in the emissions system? On face value, gas leaking on pavement should at least be an emissions concern, right? Is there 10 years warranty on emissions components?
G&K conversions are first generation 450s (<2008) so that shouldn't apply to your 451s. US Mercedes-Benz dealerships do not service these vehicles.
I haven't heard of fuel leaks being common in 451s. Many of the early "fuel leak" issues with 2008s were simply people overfilling their tanks and killing the charcoal canister.
And no, emissions equipment are just that. Leaks that develop over time don't count as emissions equipment...Otherwise you'd be able to get the dealer on the hook any time a car springs an oil leak or a coolant leak.
If every owner of a 2008 ForTwo with a fuel leak, transmission failure, or defective seat-belt filed a NHTSA complaint, someone would notice that 10-50% of a population of model-specific owners have a serious safety issue & it could be the basis for the recall. THEN the dealer would invite me in to look at my fuel leak.
It is a nearly 10 year old car, a European
car at that. Things are going to break. 2008 transmissions were fixed with better clutch plates that for the most part should have been replaced under warranty by now (and by 2010 that issue was pretty much dead and gone). The seatbelt can probably be argued for a recall but I doubt there are enough cars to justify it...especially considering age and mileage.