The ZF on that era is not electronic, on P38's and D2's they are.
In answer to your question, 90% of the problems with autos is down to old fluid. What can seem like a bad problem is easily fixed. Whether or not this will make a difference to your box I do not know, but it is worth a shot as general maintenance anyway.
I would drain the fluid, refill it and go for a short drive, 10 miles would be plenty. Come back, drop the fluid again, sump off and change the filter. Refill again with new fluid, with the vehicle stationary and engine running move the shifter down through R, D, 4, 3, 2, 1 (or whatever gears it has) and then back to P and switch off. Allow time for the fluid to settle and check the level again.
The reason for changing some of the fluid and then going for a drive is that the torque converter hold a lot of oil that you cannot drain. By changing the oil in the box first and mixing it all up you will get more of the old oil out when you drain the second time.