They will all leak at some point, then it will stop and then it will leak again. Some will leak more than others. I strongly believe that either there is not enough heat at the bottom of the pot to seat the plunger, or there is some garbage in there that prevents the plunger from seating correctly. Lot of it has to do with the type of lead you use. I have used all kinds in the past, and I've come to the conclusion the worst for those pots is wheel weights. There is so much garbage in those weights and the lead is very hard, that I stopped using them. There are some things you can try, flux your lead very heavily, turn the heat up a bit, and use better lead. I flux with bees wax or candle wax, works for me. Also I now buy my lead from Roto-Metals, and don't have nowhere near the problems I've had in the past. There are a lot of things you can try and you will get a lot of advice here. Try some and find what works for you then write it down for next time. Good Luck.