Although it looks like two hoses are on the oil filler tube.However, the large breather hose from the crankcase routes to the oil tank where a lot of high velocity oil + blowby dissipates before venting to the filler pipe. The other hose vents the oil from the oil filler tube back to the intake, catch can and/or atmosphere. Any significant hose restrictions will increase crankcase pressure and exacerbate any potential oil leaks.
Pics from a related thread:
http://forums.pelicanparts.com/porsche-911-technical-forum/958569-3-2-vacuum-leak.html
I mirrored Walt's suggestion to insert a large spring in the large hose from oil tank to oil cooler.
Sherwood