We used to own a Marklift Jobhandler. It was a 8000 pound, 36 foot reach telehandler, made in 1985. It had rotating forks, also the whole forks assembly could be slid to the left and right, about a foot each way. It was especially useful for setting trusses because of the forks maneuverability. Does anyone have any info on this machine. Looked online for it and did not find anything at all. Now it is sitting behind the shed, gave up on it after engine went, problems before that were bad brakes, stuck in first gear, very slow hydraulics, boom would settle fast. Other than that it worked fine for us.
I have seen a few at auctions in recent years..... maybe two or three. I dont think Terex supports the parts for those machines anymore. I would call Genie Industries (terex aerials) and ask someone in the parts dept and verify that. They very well could still have the parts and service manuals they can email you. If you have that it would give you a fighting chance to at least match parts. Most of the manufacturers over the years used many of the same parts on their machines. I think its going to be like finding a needle in a haystack to actually locate anyone who really knows the ins and outs of that machine. You may end up finding that its cost prohibitive to even get it going again. Many of the problems you are describing could turn into big money quick. Not trying to detour you, just looking from an outside prospective.