I managed to fix this without any manuals (but if someone can tell me where to purchase one, i would apprciate it).

I'm placing this here in the hope it might help someone with a similar issue.

The oil filter for the transmission was loose (the gearbox and mast operate from the same oil reservoir), when cleaning it to find the part number i made the situation worse, i must have disturbed the grime around the filter when cleaning it, so removed the filter and noticed that the centre mounting bolt/adaptor (screws into the housing and the filter screws onto that) was very loose.

I tightened the adaptor, fitted a new filter (the old one had a crease in the seal) checked the oil, started it up, lifted the mast right up (to remove any air bubbles) and the forklift drove perfectly. Started it 24 hours later, drove straight away, no issues and no oil leak.