Caterpillar VC60D SA diesel forklift, transmission not engaging

Hey guys, my company is in the warehousing/storage industry and one of my forklifts has been down for a while. It's an early 90's model Cat VC60D SA. For the life of me, I can't get it to engage forward or reverse on the transmission. It's a great running forklift otherwise. Initially, I thought it might be in the electrical switch, but all wiring and fuses appear fine. Since both forward and reverse won't engage, I'm leaning towards the inching pedal spool valve being the culprit. I have never taken one apart, cleaned or rebuilt one before, though, and was wondering if this sounds accurate and how it needs to be done on this machine. I've been searching and lurking for a while, but the only thing close I found was this post from 2010, HeavyEquipmentForums If anyone can point me in the right direction, it'd be much appreciated. Thanks!