John Montgomery

I have a center fill 911 ST style tank. After a fill-up when the tank is absolutely full (with say an inch of fuel in the neck of the tank and thus fuel up against the top of the tank and sender-unit seal), the fuel sender leaks. Once I have driven for 15 minutes and the fuel level drops it's OK.
I recently replaced the sender and used a new rubber gasket and torqued all nuts correctly.
A few questions:
- I noticed that one of the five studs securing the sender is stripped, it could not hold the torque. Could it be that the sender would leak if only 4 studs were properly torqued? - If so, to replace the stud, does it simply screw out of the rim that holds the sensor, or is it pressed in from the bottom?
- Could the rubber gasket be the issue? Is the original cork gasket better?

Or is the seal simply not designed to withstand the pressure of fuel pushing up against it? (and I should not fill up the tank so full)

Thanks!