Wrong, the auto's on these are excellent auto's imo.
Yes they do suffer problems, and are not very diy friendly, but manual boxes go bang as well.
It's not the fluid, does it jump up and down gears at will, more so when it is warm ?
If so all these changes are governed by a complex switch that reads speeds demands etc, these go wrong and are a whole £30 NEW, 15 minute job to fit, with a few tools, no biggee.
On the box just near the where the battery tray ends is a large connector that goes into a part on the gearbox, it has from memory around 16-20 wires in it, make sure this is clean.
If you like I will get the part number of the baddy bit.
The early vsersions of the box got a bad name as the clutch fingers used to break on the basket as they were a resin type, later and modded to cast alloy to solve the problems, the only other big problemis there is a diaphragm that controls certain speed pressures, this can tear or stick, but will lead to no drive at all.
I suspect that yours is a chronic up down violent change ?
tabetha