When I found out that hydraulic lifters may not be made in America, I started buying NOS Chevy and Buick lifters. The ones I have left now have varnish in them that makes the inner plunger stick. I take a cup half filled with lacquer thinner, immerse the lifters four at a time for a few minutes until I can push down on the inner cup. I then individually disassemble them and clean the hardened varnish, rinse them in another cup, dry and reassemble with WD 40 before installation. I do primarily 455 Buick engines, so I prefer not to pump them up as it makes the shaft rockers harder to install. I then prime the engine to pump them up. This is a picture of the trash from one lifter. It is a good idea to wear safety glasses as the clips may fly out.
Mike Phillips
Automotive Machine & Performance
Owensboro, KY
