Both my 16 valvers suffer from oil in the air filter. One has a K&N and I didn't want to ruin it with black gunk from the breather so I decided to forgo doing my bit for the environment and I have blanked off the hole in the air box that accepts the pipe and placed the end of the breather on top of the chassis leg, where it is hoped that it will continue to spill its load onto the chassis leg to prevent rust.
Incidentally, the old mk2's seem to get better with use as my smoker 122k easily pastes my wife's 50k without a problem.