Excuse my ignorance, FRiend - why did it leak by design?
Because at its operating speed and altitude the fuel tanks as well as most of the craft expanded by as much as two inches, IRRC.
Therefore, on the ground the fuel tanks would contract.
I saw it at an airshow and seeing the fuel leaks up close was different. Amazing aircraft to see fly. They didn’t put a lot of fuel in on while on the ground and generally refueled it after takeoff.
Heat expansion during Mach 3+ flight sealed the tanks.
If the tanks were sealed on the ground, the heat expansion would have burst them or the airframe.
It didn’t run on JP4, it was JP7 if memory serves, also used to cool parts of the airframe during flight.
It was built by Harley Davidson. :-P