Hi Guest!
Hey - did you know if you click on the title of a thread it will take you to the first unread post since you last visited that thread?
but were afraid to ask: 
STOP!! Never post your email address in open forums. Bots can "harvest" your email! If you must share your email use a Private Message or use the 
smilie in place of the real @
Pretty Please - add it to our Events forum(s) and add to the calendar! >> 
racingenglishcars
Darth Vader
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Check out what Scott did with his.
https://www.britishcarforum.com/bcforum/ubbthreads.php/topics/443655/4
You don't need to be so elaborate with the pcv valve, but installing one should take care of reducing crankcase vacuum.
That check valve you mention may not be working correctly, or it might be an attempt to reduce crankcase vacuum.
If a vacuum is produced within the crankcase, it will help prevent oil leaks, but if the vacuum is too much, it can hurt seals and will try to take outside air from any place it can get it, like your dip stick hole. Maybe a breather would help.
https://www.britishcarforum.com/bcforum/ubbthreads.php/topics/443655/4
You don't need to be so elaborate with the pcv valve, but installing one should take care of reducing crankcase vacuum.
That check valve you mention may not be working correctly, or it might be an attempt to reduce crankcase vacuum.
If a vacuum is produced within the crankcase, it will help prevent oil leaks, but if the vacuum is too much, it can hurt seals and will try to take outside air from any place it can get it, like your dip stick hole. Maybe a breather would help.