Happijac lubrication

Great post. If the swivel at the bottom of the acme thread is badly rusted, the black tube will torque twist. This will cause the paint scraping because of corner to corner rubbing. This will also cause lots of groaning and grinding and popping noises. I lubricated my 4150 with 90 weight hypoid oil. with the black tube secured in the vertical position, I extended the screw as far as possible and then poured the oil(a few drops) onto the nylon nut and let it drain down. This takes several hours. I repeated this several times. Working the acme thread rod up and down, it eventually was loose enough to turn with only my thumb and forefinger. After everything is loose, grease the whole rod.
The nylon nut can fail and become stripped. The steel safety nut should prevent catastrophic failure. Similar nylon nuts are used in adjustable hospital beds and they do fail. The nylon nut can be replaced, but you will need advanced machining skills. For all that is at stake, replace the whole jack instead. A new jack is cheap insurance.(Oil the new jack with the hypoid oil.)