So you are talking the shaft seal, not the face gasket? Right? I guess it's the shaft seal if you bought 3 pumps. It does seem like you are putting too much pressure from belt as BC said. Orrrrrrrrrrrr..........pump pulley not aligned on same plane a crank pulley....orrrrrrrrrrr a pulley is bent and wobbling a little.

If you are taking them back for warranty, don't do that anymore. Get your money back and buy the next one at a different brand of store. Different brand of pump. Remember what Albert said.

BTW, what is the purpose of the silicone in step 8 of instructions?

Right is right, even if everyone is against it, and wrong is wrong, even if everyone is for it. - William Penn