Genie TMZ 34/19 manual leveling issue

I've recently bought a 1999 Genie TMZ 34/19. It is the manual leveling type. I am having trouble with the left front outrigger. No matter what I do, I cannot get it to "read" level, even when the level bubble is perfectly centered. Of course, the controls won't function if the machine thinks it isn't level. The one time I did get it to work, it suddenly became "unlevel" with the bucket in the air. It's only the left front, the others are fine. What could cause this?