hi have a Komatsu approx 1990 FG20T-11 forklift in australia.
machine is in good condition, starts, runs,everything works, except no forward torque. gearbox definitely engages but even a slight incline with stop it moving. revving more does get slightly more torque
oil in gearbox is dark.
reverse seems to work ok, lots more torque.
im guessing clutch plates worn in forwards but ok in reverse? would a faulty torque converter fail in both directions?
anyone have access to workshop manual and service manual or parts lists for this model, as will be removing gearbox myself if thats what is required. happy to pay, just can't find them anywhere! can this be removed without removing front axle? i assume, engine out, then gearbox?
thanks for any help/ideas!

edit manual available for other model, any idea which models will be similar enough to use manual for gearbox?