I'm thinking Jwooky might have the leak source. I can't see the trans creating pressure with the air on top of the oil being past atmosphere, where I would think you'd have to expand the air above the oil. Whereas I can see two failures without adding the pressure variable into the mix.
Seal shows new, but did they replace what rubs on the seal? So where is the other part the seal rides on? Groove? Seal can't set the harder lip onto the worn grooved surface? Second would be ball collapse and that would drop the shaft and and have an air gap at the seal.
So disassembly wise, I'd pull the part the seal rides on, rather than pull the trans and pop the bearing out? See where I'm going if that sleeve can be replaced the seal rides on?