problem with auto gearbox in TD 60 series cruiser

Hi - considered posting this on LCOOL site, but they seem to focus on late model cruisers so thought I'd try here. A mate of mine has a 4l turbo diesel 60 series with auto gearbox. I'm pretty sure it's only got about 250,000 kays on it, but he was convinced by some transmission nutscratchers that the input splines on the gearbox lacked a bit of meat so he should get it recon'd - at a cost of $5K! Anyway, after the 20,000 kay warranty period had expired, the box developed a problem whereby it wouldn't change up from first until it had warmed up. It has now developed a problem where it overheats and won't engage - i.e. after about 50 kays, go to take off from standing start and just moves forward slowly - reverse no problem.

I'm trying to convince him to fork out the $100 to get it power-flushed as a first option although the overheating may suggest something more serious like something rubbing, or perhaps just a blocked tranny cooler. If the fluid/cooler service doesn't work, how easy is it to convert one of these to manual given that he's not interested in forking out a couple more grand to get the mechanics to remove and open up the auto for a looksee...

Thanks