I've never quite understood the reluctance to use MAYDAY demonstrated by some quarters of the UK Mil. It doesn't cost anything and, provided the aircraft has a genuine emergency, no-one other than crew room (and internet) pundits will criticise. It gets you everything you want from ATC (ie mostly silence) - even if the immediate assistance is simply changing your clearance and arranging priority for landing.
Splitting hairs about what is a PAN and what is MAYDAY is all well and good in the familiar Swanick Mil environment, but many parts of the world have never heard of PAN. Even if they have, the UK Mil has decided to change the ICAO PAN PAN x3 to PAN x3. You can pretty much guarantee that any such call will be followed by "Are you declaring emergency?". At least MAYDAY is universally understood.
In my view, high pressure fuel spraying where it shouldn't is serious danger and not just a condition concerning safety.