Wow. Someone has a bongo as old (and knackered) as mine

)
I bought mine in Feb. It's also a 1996 Diesel Auto.
It has 200,000km, loads of rust (now fixed), leaky cooling/overheating (current project), leaky ATF cooling (parts on order), blowing mid
exhaust (now fixed), broken cold start
vacuum solenoids and hoses (now fixed), and my gearbox also jumps a bit from 1st to 2nd but fine on 2-3-4.
I'm currently concentrating on the cooling
system as this has been a showstopper but intend to do the gearbox next.
Can I be cheeky and ask how much you paid for your bongo? (just so I can get an idea of what I should have paid for mine as I feel a bit robbed)
Is you HOLD light flashing? This indicates gear trouble but only works if ECU can read the fault. Does your HOLD light come on when you press the hold button on the stick? (Just checking the bulb works).
It could be a solenoid issue as there are 4 in the box. 3 do the gear changes and one does the clutch (in layman's terms). If one is worn out or blocked it can cause this. If it's a mechanical/hydraulic fault then the HOLD light wont show it as it needs electrical signal (or lack of) to detect fault. Cleaning the whole lot may help. Try dropping the sump cover and removing/cleaning the filter and topping up with fresh ATF.
I'll keep an eye on your progress as it may well help with mine.
Good luck getting it all sorted.