Two types, tall dry motor(early) shorter easier to rebuild (later type)

If you have the later, try to soak it in a gallon of gas for a few days to swell the seals.

I just had one dry out from cleaning and drying the fuel system, (1965 220SEb) for 2 months. and it leaked upon filling the tank.
After a few hours it stopped and has remained stopped.

You may not need a new one of the motor still spins.
also remove and clean the one-way valve at the pump exit.
Please report back, a lot of these pumps are replaced needlessly.