A few years back at the MVPA convention in Petaluma, CA someone had mentioned that old Cadillac V-8 lifters were very similar to the White engine and may work. I bought a few used ones to compare and the body and unit are different but I think the plungers are close enough to be interchangeable. In a panic I checked eBay and found some at a reasonable price and ran out to the garage to get the Cadillac ones I have to compare. Again, the plunger was not compressible. OK, so I put the plunger in the unit and guess what. It was compressible!! WTF!! Sorry for the language but this stumps me. So, I tried all 12 on my spare engine plungers that were all rock solid by them selves and guess what, they all compressed!! WTF?? OK, I re checked the three bad ones I removed from the engine. They compress!! I have no clue why only in the unit they compress. I do not see a valve in it but will retry to install one tomorrow afternoon and see what happens.