What years of X5's are most susceptible to the dreaded oil separator failure?

The job is fairly easy, but the access to these parts is limited. It doesn't require any special tools too.
There is actually no need the change the dipstick or separator, they just need to be washed. The thing is that you can't see inside the separator, so it's difficult to tell wheter to change it or no. It depends on your driving habits, but changing it once a year should be more than enough.
Also, checking the inside of the intake manifold for sludge it a good idea too.