[Deo]

Can't find the video I've seen but you've got the info you need in the thread already - the technical documentation that Rondeo linked to, and the quote you got from Ford shows the rebuild kit (cover kit) that I was thinking of.
Basically there are some metal 'gaskets' which cannot always be removed without damage - perhaps if the tech goes slow and is very careful, but I suppose Ford did a cost-benefit analysis and decided it was more efficient to replace those bits each time.

You are correct, if the trans fluid is being changed you should put a new filter on too, they are relatively cheap.