Hello guys

I'm just a simple mechanic from Belgium who has a small home shop if you can call it that way. I have a Nissan EH01A15U small forklift, I believe early 90s.

It started with having no reverse. Some fidling with the shifter linkage seemed to do the job. The next day I had reverse nor forward. A lot shifting (and the engine warming up?) later it worked again but I decided to change the transfluid and clean the filter. After this it still worked, but today again no movement. In the short period I had the Nissan I always had to give some revs until it broke free as to speak.

After some searching it seems like the culprit could be the inching/declutch valve, I have 2 brake pedals. The left pedal moves a pivoting arm on top of the trans, about 90 degrees. When disconected I feel no resistance at all in this arm.

Any advice? I'll probably will need to remove the top of the trans?