For one thing, it’s not great for the environment to do that. Some cars are tuned in such a way that any metered air that is vented to atmosphere (even from the PCV system) could cause issues with the air fuel ratio, leading to symptoms similar to a vacuum leak. I am not familiar with the Micra so I don’t know if that car has a system that is sensitive to that type of thing.

I’m not real familiar with G80s, but I know Subarus don’t handle PCV venting well without being tuned for it. For instance, an IAG competition AOS requires a tune because it vents air from the PCV system to atmosphere. Your catch can setup sounds similar to me. IAG’s street series AOS on the other hand recirculates that air from the crankcase back into the intake.

Speed density setups (cars that use MAP sensors instead of MAF sensors) tend to be a little better at handling that kind of change without any aftermarket tuning. If your fittings are tight enough, you shouldn’t have to worry about vacuum leaks per se, but you might need to be concerned about venting metered air that is supposed to go back into the intake. This could throw off the air fuel ratio if the car is unable to adjust for the change on its own. Just something to look into, hope this helps.

There is often a seal or grommet around the PCV valve. Could this be the leak you are experiencing?