1996 Mazda 323 noisy lifters and oil leak

Hi
i have replaced the hydraulic lifters and still noisy at start up especially in the morning, I gave the engine a flush before the next oil change but the problem still unchanged.
also, the rear main seal leaking, replaced3 times in 1 week tried 2 different aftermarkets brands, last seal was genuine from mazda, all the same. After reading on the net, I came across someone mentioning the pcv valve may cause real main seal leak, I went and replace the pcv valve, the next day I found an oil stain under the car as before.
please assist, I need some good opinions here, my mechanic of 27 years experience has never came across things like these.
there is nothing worse than spending money trying to fix a problem and does not get fixed
what else could have been the problem. Please note when we replaced the lifters, the head was removed and sent away for machining and pressure test and had new seals and gasket replaced as well

thank you
bernard