It's a Yale 5000 with a 3 section mast. We had a forklift company take a look at it and they just scratched their heads. They soaked the tracks down with lubed and checked the channels - said they looked ok. We bought the machine used about 5 years ago, treated pretty easy. Had the seal replaced in the center cylinder a year or so ago. It was leaking.

I think it would be with the hydraulics because the upper mast sections begin to move up before they are suppose to. (before the lower section reaches it's full extention)