why are my hydros STILL leaking?

I have switched to ND 30wt oil, put in the good parker polypack seals, and it still started leaking again after about 1000 miles... what's the deal? what else could it be..

i was thinking it may have been the heat since it got to be almost 100 here today but the seals should still keep the oil in the cylinders right???

any help is appreciated.

here is a pic of the type of cylinders i am using