I have read endless threads concerning slow leveling jacks returning to the up position and yes there are many reasons for this problem. The one suggestion that seems to get the most argument is this idea of lubricating the exposed cylinder shaft on each jack. After much experimentation, I can tell you that wiping down each shaft with automatic transition fluid (ATF) can make a big difference in the retraction time. My assumption is that the fluid lubricates, softens and cleans the outer seals...
