From the manual "Automatisches Getriebe 722.3", it outline the following steps:
1. Insert Teflon ring with grease in groove of brake band piston B2. (looks like it is already on the new part).
2. Insert thrust pin.
3. Install new O-ring.
4. Insert brake band piston B2 with thrust pin and at the same time make sure that the thrust pin of brake band piston B2 is installed in brake band B2.
5. Press in brake band piston cover B2 andd install locking ring.

There is no mention of any sealant.
Good luck with your project.

__________________
Shane83SD