Read this is a good mod to prevent toxic,corrosive gasses re-entering the engine?
Especially if the breather is venting somewhere other than back into the airbox. There was one of those on my Steamer when I had it.
It does vent back into filter housing,then back into engine,without passing thru filter? I'll check on my filter to confirm.
I use one of these on the Thruxton, seems to work well, I can feel the warm air but any escaping oil mist is undetectable.