Ahh yes, the ol' jg earwax "grease"
Sounds like the selector teeth jumped a couple of positions on reassembly, the joys of getting a v3 box into a reciever. Best method is to lie it on its side so gravity hopefully holds it in place for you.
Whilst i realise it's a contraversial opinion, i'm really not a fan of the prommy purple, it's ok as "standard" rubbers go but not anything special imo.
If you're running a unit as good as the cu then i'd be strongly suggesting the maple leaf macaron+omega nub combo, that'll have no trouble lifting the heavies.