Also there is a product by Gunk at flaps ,called Valve Medic. The bottle
says it can fix it in 5 minutes, or you have mechanical issues.I have used
it a couple times with good results. It must be a solvent that disolves the
varnish and crud that collect in  and on the lifters.And somekind of
lubricant too.Hydraulic lifters are machined to much tighter tolerances
than most other engine parts. The parts fit tighter and varnish can change
the dimentions or cause sticking.

 I think this is why hydraulic lifters were so long coming in foreign cars
(besides price, and durability).In third world countries, oil dosent get
changed often enough, and hydraulic lifters would get clogged up.The world
is getting richer now, and most owners can afford oil changes and repairs.