Fuel Sender leak

[Taxidodger]

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 (except one)
A couple of 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 on the tank 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?

Thanks!