Just to add to what Stuart told you he knows about things he has helped me ,,,, I have a Walker floor jack i have for 25 years are more got to where it wouldnt lift and i got a lincoln seal kit and put it in been working good for years (A spanner) sure helps on the nut didn't have one ...even if yours is not leaking i thought i would pass this along and have good jack stands !! after living over one fallin on me i think of that ever time i get under one .
