The small brass vent tube nipple was not very attractive, so I decided to replace it with something better. I found a company that makes a AN-3 fitting with a 1/16" NPT end and purchased two (they come in pairs).
Here's the fittings.
Up close, showing the size. I also ordered a corresponding 1/16" NPT tap.
Here it is installed on the transaxle. I dipped the tap in grease and laid the transaxle on its side to tap the hole, also watching the inner shield piece in case it rotated. It didn't rotate, which is good since any rotation might cause some interference with the ring gear.
I also replaced the front seal. It wasn't easy to remove, so I used a small bit on my Dremel and ground out the steel seal ring.