The CDR has three holes in it.
The big one at the top and the big one at the bottom that are plain to see, but there is also one in the back of the diaphram housing that is very small.
The diaphram is pressed toward the pinhole by a spring.
When there is air/gas pressure in the valve, the diaphram is pressed toward the pinhole where it already is and nothing different happens.
When there is vacuum in the CDR, the diaphram is sucked away from the pinhole and blocks the flow of air/gases through the large holes.
At idle, the CDR is a wide open orifice that allows crankcase gases to travel through it into the intake to be burnt. The only time it is closed is in the presence of vacuum which could be caused by over-revving or a maybe a clogged air filter.
I commonly see the missconception that a bad CDR can cause smoke issues. When really the "problem" is that blowby from an increasingly wearing engine passes through it into the intake and can make smoke, but the real problem isn't the CDR itself but the blowby.
A bad CDR will have a bad diaphram and therefore won't close under vacuum so I could believe it could cause some smoking at high rpms, but if the smoke is present at idle then the CDR is not the culprit.
Personally, I would strongly recommend against cleaning it with anything harsh, as the rubber may be damaged and therefore cause the bad CDR.
Cleaning it is only a function of removing the buildup in there so that the gases can flow through it and so it can properly seal them off under vacuum.
I think I would try either diesel or maybe even safer would be a good ATF soak.
