I have used a 7.5" Ford IRS center section, flipped over, as the basis for the rear end on our trike. It works great, except...I installed a vent in what would be the top left corner of the housing. Looking from the inside, it would be almost to the end of the spider gear housing. Anyway, I keep pushing gear oil out the vent. The last system was 1/8" pipe fitting with a 1/4" hose barb, 1/4" hole through fitting, about 6 inches of hose, with a little breather on top. The rear end pushed out gear oil. I'm now thinking, upon looking at old photos, that there was no vent in this center section before I started. Is there/was there a vent in the discarded cover that has long since bit the dust? Do I need a vent? And no, it was not over filled. It had the prescribed 1 1/2 qts. Thanks for any help you can pass along.