Crank case Breather/oil seperator - How often ?

Q.
The car will be going in for a full service in the next week or 2 and I am just wondering about the Crank case breather.

I replaced my filter with an Oil seperator when I got the car 8k miles ago.

How often should this be Replaced ?

I have been googling it and getting different info.
Every service.
Every second service.
Every 30-40k miles :huh:

I replaced it every second service on the e39.

Anyone have any idea or info.

It doesn't really need to be replaced as such once it's not the loo roll type. I normally just take them out and give them a clean.