Australian auto 760Ts came with the ZF22, they are known for slipping and shifting problems. They are very sensitive to fluid level and condition. Normally when they start having issues it's too late to chnage the fluid though, the valve body starts to have issues that cause them to slip or hold gears. You can fit another valve body or rebuild the original but it doesn't guarantee it will solve all the issues if the internals have other wear or damage. Rebuild kits are easy to get and they are a relatively easy auto to rebuild. They are used on lots of other cars, bmws, land rovers, etc.
I've delt with 3 of them in 760Ts in the last few weeks, the first one worked ok but would slip under boost, the next one we fitted was apparently a low Km unit in good condition, but it slips so much the car can't be driven. Another 760T I have seems to have a rebuilt one in it which works ok after some work, but they never seem to last very long.
If you're not interested in rebuilding or replacing the ZF it's probably best to fit an AW71 from a later 700. As long as you have some of the related parts to go with it, tailshaft, cross member etc. They bolt in. They are a lot more reliable and easy to get.
This is what the ZF looks like