Welcome mate. On those older Linde units the K1 contactor not pulling in is usually a control side issue rather than the contactor itself, especially if you've already replaced it.

First things I'd check:

Is the coil actually getting voltage when you key on and request drive?
Seat switch, brake switch and direction lever interlocks. If any of those aren't made, K1 won't energise
Fuses and control relay upstream of K1
Wiring back to the controller, sometimes you'll get a break or corrosion in the loom

Those machines rely pretty heavily on the safety chain being intact before the main contactor closes.

If you can't track down the exact schematic, try looking at similar 335 series diagrams, they're often close enough to trace the circuit. This page on an electric forklift range (https://lindemh.com.au/products/electric-forklifts) can at least help you compare general layouts, even if it's newer gear.

If you've got a multimeter handy, start at the K1 coil and work backwards, you'll usually find where the signal drops out pretty quickly.