The trans vent helps stop trans leaks and has no bearing on the oil in the airbox issue. Actually, I thought that mk11 machines already had a trans vent from the factory (unless it’s just later ones)? The oil gets into the airbox via the engine breathing system. The factory have had a number of different iterations of ‘fixes’ for this. All I can tell you is that the latest ‘fix’works, at least it does on my bike. Without knowing exactly which ‘fix’ your bike has already it will be difficult to suggest what you need to do. So unless you’re quite knowledgable on Norton fixes in general I suggest this would be a difficult and perhaps rather frustrating thing to attempt a DIY fix for. Far better if you have a trusted dealer or mechanic that could do it.