So I see lots of conflicting information on the internet about catch cans and blocking the PCV ports. I have researched for days if it is ok to block the ports or not and have gotten nowhere. So here is my personal experience. I have measured vacuum pressure in the valve cover and the intake manifold vacuum lines with and without the PCV valves blocked and there has been NO DIFFERNCE in my pressures. BUT please keep in mind that my engine timing is off and may effect those readings. Also my catch can at the moment is collecting nothing but moisture! I will redo the test once my new timing chain is installed by DetroitTuned and try to put this puppy to rest once and for all. In the meantime please know that my mechanic says that the PCV ports should absolutely NOT be capped.
Your mechanic does not understand how the MINI's PCV system works, it is different from most cars. The N14 engine has two PCV valves. The rear PCV valve, to the throttle body, opens when the intake manifold is in vacuum, this is when the turbocharger is not supplying boost. It closes when the turbocharger is supplying air pressure to the intake manifold,think of it as a one way valve. When the turbocharger is supplying boost it causes a slight negative pressure on the PCV valve to the turbocharger inlet, that and a small build up of crankcase pressure, opens the driver's side PCV valve and allows the turbocharger to draw a vacuum on the crankcase. When you block off the rear PCV valve to the throttle body, all of the PCV valve function is performed by the PCV valve to the turbocharger inlet, this does not hurt anything as the valve is very sensitive and it will not allow crankcase pressure to build up. Sometimes that valve will fail closed, this will cause the crankcase pressure to build and cause oil leaks at the crank seals and the head cover. a new head cover will solve the problem. I have been running my N14 engine with the PCV valve to the throttle body blocked off and an oil catch can on the PCV line to the turbocharger inlet for nine years with no problems. The PCV line to the throttle body is the principle source of oil mist to the backs of the intake valves where it burns and chokes off the intake ports. That is why you put an oil catch can on the PCV line to the turbocharger inlet, to help keep oil out of the intercooler.
Right now I have a BSH catch can set up like @DneprDave. I’m going to give this catch can a try. http://teamrxp.com/products/bmw-rx-dual-valve-pcv-evacuation-system Here a video of how it works.
Like Dave, I ran the BSH CC with a BSH Dual Tap blocking the rear PCV port. I used one tap for a boost gauge and the other for a Forge BOV/Diverter. I had it installed for about three years and it was still working fine when I traded the car. This is a picture of my setup.