The Subaru transmission has a small case breather built into the dipstick. Since the dipstick is no longer able to be used and the dipstick tube is sealed, a case breather should be built into the transmission in order to relieve pressure build up.
Subarugesars supplies a dipstick cover with each kit. This is a hi-temp silicon cover that ensures the oil flung up by the reversed ring gear does not get pumped out of the transmission. In order for the transmission to ‘breathe’ once the oil gets hot and expands/aerates, a breather hole in the casing is required.
The ideal location for the case breather is in the rear of the transmission case, as far out of the way from flinging oil as possible. The suggested case breather consists of one hole just above where the nosecone joins the main case — on the starter motor side. This area is a hollow casting area protected by the horseshoe.