Take a break from taking bits to pieces and have a look at the condition of the brake bands. You can lift them out from between the gear set and the plastic holder. If any part of them are cracked, pitted, or damaged you need to replace them. If they are worn thin you also need to replace them. Here are some pictures of some knackered brake bands.
If anyone has experience of relining brake bands please contribute to this thread
Brake band relining - a question for the adventurous. I'm interested in learning how to do this. I was told that the brake bands in this transmission are paper lined and that it is in principle possible to cure the glue in a domestic oven... sounds like fun! You might think this is a bit mad until you find out that most parts suppliers want you to pay in excess of one hundred and fifty Euros per brake band (cost more or less correct at the date of this post).
If you replace your brake bands with new ones soak them in clean ATF for at least an hour before you fit them. If you are reusing old brake bands clean them as best as you can and then soak in clean ATF. You want to keep the inside of your rebuilt transmission as clean as possible. Think surgically clean rather than “oh bugger it that'll have to be good enough”.