the best thig to do here is to get the model and serial for real help so post again after u look at it

if there is no data plate then look for the serial number stamped somewhere on the frame
newer cats have it by the battery tray older 1s are on the front cowling in the area of the right hand tilt cylinder as if ur sitting on the machine
these stamps are usually not hard to find but paint may be covering them if the macine has been sprayed over

first is it stick or auto (clutch or inching pedal)? [pedal on left]
clutch does not apply brakes inching does

if its auto check the fluid if its low look for where its leaking (main seals, radiator tranny lines, filters)
check for a misadjusted inching pedal as this can make the tranny slip

if its stick and a model example v50 check clutch adjustment and u can inspect the meat on the cluth easily via a plate over the clutch housing
some are oil cooled some are not

but b4 all that the age of the machine would prob decide where u go from there
cat has been makin forklifts for a very very long time
they were orig made under the name towmotor and that ended in the early 70s so stay away from them
also there are crossovers between towmotor and the cat brand name they start with model numbers 422s etc again stay away still in the 70s

after that was models like t40 and v40 with revision abcd and maybe e? not sure these are ok but are starting to get old as they were produced thru the 80s

after that they merged with mitsu in the early 90s those machines are model that start with gp (pnuematic) and gc (cusion[solid] tires) these id consider fixing depending on the overall condition and at a price like that prob worth fixin if major work is needed