Although I've never opened a european trans up yet, (I'm told by some that they are a different world) I have taken classes on rebuilding domestic/asian units, and have done several GM and Ford successfully. What I have always done in the past, with the gaskets, clean resudue from the metal facings, and smear a film of vaseline (or dab strategically) and press the gasket onto it, usually holds quite well, used or oily gaskets won't hold as well, but usually you can get them to stick long enough to get it together. Check balls I have found change with year and vehicle model, in the same model of tranny, I don't know if the same is true with these cars. I usually look at the pictorial or description of how to place them in the manual and compare carefully before removing any, and if there is a variance make sure it gets duly noted beforehand. I would recommend replacing all seals and gaskets, & servo/piston lip seals. Disassemble the clutch packs and inspect the frictions and steels for wear and heat spot discoloring (heat spots mean the steels are warped and need replaced so as not to drag on the frictions.) Also be sure to check your splines and hubs to be sure the teeth on the discs arent chewing notches into them. I could go on with a lot more, but this is the basics of what I've seen generally in the rebuilds I've done, of course, check tolerances and bearings and such as the manual should recommend. Just take it slowly and carefully and you'll be fine. One more VERY IMPORTANT thing, try to your best to separate the valve body with out damaging, or at least minimizing damage to, the gaskets. They need to be checked against your new ones very carefully! Many a time I have found the rebuild kits come with a different cut gasket and have had to reuse the old ones. They usually have an identifying munber, or notch on the edge, or color stripe to help identify them also, but ALWAYS compare them. Even one differing hole can cause disaster.
-Chris