I replaced a glow plug on my 2006 diesel (BKD) car last week in order to cure a glow plug warning that had been present in my VCDS logs for about a year. Whilst I had the rocker cover off, I was curious to know the state of the PCV in it. As it appears to be sealed inside the rocker cover, I simply blew/sucked from the breather pipe. It was as though I was blowing/sucking through a clear pipe. Is this normal? I thought that there was a membrane inside so should have felt a little pressure. Is there a test that can be done for these?