I do a lot of rebuilds and so far not to many have needed new clutches unless there has been a seal blown and thats why I took it apart.
As far as reseal kits all the kits I have gotten are MB factory kits and have the new seals in them.
There is an alternative if you are going for frictions and that is IPT. They are building a super tough tranny for merc. and chrysler on this platform. They also sell a banner kit and valve bodies. Prices are about the same as mercedes but the clutches are kevlar and like the previous post said you can get new bearings and should. The one way was updated to have more rollers. Twice as many if I remember. The ones that I have seen fail recently look normal also but do not hold? It is hard to know what the right choice is though on rebuilds. They cost a lot and you can go get one already rebuilt with a warrenty for less than 2500. Not MB of course. To check the clutch packs it is pretty hard to do per the book without a lot of special tools. But if you get the specs you can just press down on the packs and check. This is a good indication of your clutch material.
As far as even doing the seals, you will need the special tool to take the pistons apart. Check out SG Motorsports. He is a buddy of mine and sells MB
shop tools from an aftermarket supplier. Good prices. j
I am getting to the point of just buying newer transmissions from the junkyard or off craigslist. I just priced out a 722.6 from a 97 e420 for 950.00
I can buy late model stuff for 1200 for small nag. and 15---1750 for large nag. That way you get all the updates and a good transmission.
Shout back if you have more questions.