8# sledge hammer work all morning. I soaked the tubes upside down overnight with Kroil. Beat on the foot all morning trying to separate them. At first maybe 1/8" per whack. Then it got better and better. Actually bent the foot and cracked at least one weld. But I got them separated. Lots of dirt and excretement. Collateral damage was the little white plastic tab opposite the disengage lever. I watched a youtube of a guy taking the tubes apart and he attacked the little tab with a screwdriver and a hammer. So I did too. Should have known better, he didn't know a circlip from a cotter pin. Also the o ring came out in 2 pieces.
I might pour some CLR in the upper tube and see if it cleans up.
I'm turning the acme rod and soaking it in penetrating oil to clean it up. It seemed surprisingly clean.
Sent an email to Happijac requesting parts.
Will take the other front jack off and at least start soaking it.