A/o s
 

Has anyone taken the plenum off, cleaned etc? having this off does it make it easier to get to the air oil separator?

There is a huge amount of help here https://www.pelicanparts.com/boxster/boxster_tech.htm and on YouTube.

AOS..is actually easy it takes some time but Ive done it twice, 1st time took about 2 hrs..2nd time a hour and 10 minutes maybe..My tip would be...if the hoses are warm they disconnect much easier,..pull the rear wheel and of course the panel you can reach everything..