ok i did a compression test about 2 months ago when i did my water pump. then it was at 185-170-170-170........... now i recently did one because the car hasnt been pulling the times it was in the beginning of the season. now, 185-175-165-155. can anyone tell me where i am loosing compression at? is it the piston rings? or maybe could it even be a leak in the headgasket that could cause it??? also if it is the piston rings what procedure would i go through to replace the rings since i am replacing rings should i just get a set of CTR pistons or an aftermarket set???

any help on what might it be would be is appreciated

 

also what is a good site to buy piston and ring set or even a pistons set w/rings and rods?????????