Engine Smoke

[oldschool20]

I have tried to do a search on this problem but not having much luck. I have a 94 s10 4.3 with 178000 on it. Engine runs fine but about 2 months ago she started smoking. The weird thing is it starts after it has been running a while not when its cold or first started. Some one told me to check the oil drain holes in the heads so I did and the rear hole on the pass was clogged some and the plug for that cyclinder was the only one that showed signs of burning oil. I have 150 psi compression on all other cyclinders and 145 psi on the oil burner. The smoking stopped after I cleaned the hole. I added about 8 oz of Marvel Mystrery Oil in hopes of a little sludge cleaning. Then I changed the oil about 2 weeks after and added another 8 oz of Marvel. The smoking has returned and this time its a little worse. Any ideas?????

Any body?????