So, you're angry Nissan aren't covering parts due to the wrong fuel being used?
Would you expect them to warrant a diesel pump of your customer filled it with unleaded?
The wrong fuel is the wrong fuel.
Don't listen to fuel manufacturers, they're trying to sell.
Listen to the engine manufacturer.
If they say don't use it, don't.
Or, take the risk and POSSIBLY pay in the end.
Regards, the angry mechanic who has to deal with customers who believe it's everyone's fault except theirs.