The control valves go bad on these before any more damage occurs, it may pay to dump,refill,dump refill till clean (around 17 litres , do it via the hose going to the cooler,dump a litre,fill,dump etc) reset adaptation.
Right now (and I'm no expert) you may be able to swap in a modified valve body for it from Level 10 Transmissions in USA. They do core swap on their units, talk to them, they will be helpful being so far from them.
The gearbox can be rebuilt.
Where do you live?
If Melbourne, Berry Motor Group or Voldat or Mason's Prestige can point you to a shop/do the removal etc.