Yep. Opening the vent to atmosphere may make the problem worse rather than better. I just wonder if, as well as sucking damp air in when bike cools, will it let the moisture out again?
I'll look out for that PCV valve.
You're probably right, in that the only real solution is to use a CZ 125 for going to work – or better, a pushbike. Those big cars that are only doing 4 or 5 mile trips, used for school drops and shopping, must be getting wrecked inside.