Certainly not an expert on differential vents here either bit is seems to me that getting the vent high with a long hose may help this problem. Speedway has a kit - New Longacre 1 1 2" Clamp on Billet Rear End Breather Vent Kit w Hose | eBay but you could duplicate this with a nice stainless hose and a billet vent cap mounted as high as possible allowing the oil vapor to escape the rear end but cool and return as well.