Where are the cracks starting? If it is down towards the nut that holds it in place I would say you might be over tightening it.
As for the center post o-ring coming out the base you are over tightening or you have the wrong size. Try not to crank it down so much just till you feel it give some resistance.
The first one was broken around 1/3 up from the bottom, the second one was broken in 3 pieces. Im sure that the oring was due to over tightning and that i dint use vaseline. So my guess is that i may have torch it to much, if its even possibel.