Unless you have a pit or hoist, removing the gearbox aint for the feinthearted as it's no lightweight especially with the transfer box attached. Could be something as simple as a seal gone but if it is inside, my advice is don't even go there as autoboxes are a pig to work on and you won't know how it runs unless you have a test rig, until it's refitted. The boxes on P38's tend to be pretty bullet proof if they are looked after.