<VV> Oil Filler Cap Leaks

[Carl Kelsen Arlette Pat]

G'day Everyone,
I have read in the Corsa Corvair Technical Guide that oil can leak from the oil filller cap as a result of oil being thrown under pressure, up the filler tube.

Wanting to avoid this and the resulting mess I followed Bill Clemens suggested simple solution to prevent this oil leak. Simply plug the oil filler tube with a rubber bathtub plug.

I have obtained an ideal size bathtub plug that fits neatly inside the filler tube and of course can't be seen once the Oil Filer Cap is in place. So perhaps this will work well? However I wondered if there are any down sides to doing this? For example, does the engine need to vent through the oil filler tube?

If there are no nergative effects from sealing the oil filler tube in this way, then it's certainly an easy fix. What's everyone's view?
Regards from Australia
Carl Kelsen
RHD 1965 Corvair Monza convertible