From an ex Clark forklift service manager, do NOT buy the hydrostatic unit! It is expensive to fix and takes special equipment to diagnosis it! We had fleet of Clarks and two of the hydrostats, they were constantly having problems, and we finally sold them to wholesaler to get them out of area! The clark automatic is great transmission and will outlast the forklift, the hydrostat is not so.
The transmission is adjusted by a handheld programmer and only few dealers ever had one. See if seller has the hand held programmer!