if the transmission case has no breather on it then the breather is probably in the dipstick itself or the filler cap (if it has one separately from the dipstick tube)

plus as was mentioned , i too have seen factory fixes that included adding a hose with a breather on it that is incorporated into the dipstick or extending the origional breather up higher than first designed.

I know on one of the 25e-3 or e2 series there was a update to the dipstick tube and extra hosing that needed to be put in place for the same reason cant remember the specifics sorry try your local dealer