Valve stem seal function, leak down test

I bought some high flow used heads. In order to clean
them up I pulled a valve out. It felt bad coming out,
seemed like small pieces of brass shavings came along
with it (the keeper end seemed to shave brass off the
guide as it came through). I replaced the seal,
installed the heads. Have run for 5K miles struggling
with oil loss and dirty oil. Compression checks good.
Leak-down testing showed some cylinders up to 12%.
Mechanic said this is in normal ranged, other
references suggest anything above 8% indicates bad
valve sealing. By installing a breather on the
driver's side valve cover I eliminate excessive
exhaust smoke, but it leaks oil all over. Questions-
Does leak-down testing indicate if the valve guide
seals are bad? Is the 12% leak down indicative of bad
sealing? Can the constantly dirty oil be because of a
bad valve guide seal? Are the drivers and passenger
side valve cover compartments essentially connected
via the intake, see the same pressure?

thanx for any help,

Blowin Smoke in CO,

Brad87TR

heck gm allows 20%, ford allows 25% as a rule....

u might need new or knurled valve guides and of course umbrella and oring seals...