distributor leaking???

i have a d16a6 motor. with about 130,000 miles on it. i noticed that when i take the distributor cap off there is oil leaking from within the distributor. and i guess pressure caused the distributor cap gasket to pop out on the bottom and oil is leaking out so the oil is not building up within the the distributor cap. my father in law told me that i need another distributor so he went to the junk yard a found another one and installed it. i thought that he had fixed the problem but a couple months later i looked at the distributor cap gasket again and noticed it popped out from the bottom and oil was leaking out again. can anybody tell me what could be causing this problem??

it is probably the dizzy o-ring. you can get one from teh dealership or take the one off your dizzy and take it to napa and look at their o-ring and find one that is the same size