Actually I have owned three pumas and they all suffered from this problem at some time and I never found the clear cause until now.
Having done some research I have discovered the root cause of this annoying issue. Actually there are two main causes:
1. A blocked foam filter at the end of the rocker cover breather hose (in the air-filter housing) causing pressure build up in the rocker area
2. The damn non-ford gaskets that every garage fits as standard (because the Ford ones are not cheap) never fit properly and don't seal adequately - never use these!
Additional sealant is a messy fix and will sometimes fix 2 but if 1 is present then it will soon begin leaking again as I found
Fix:
Clean the small filter element in alcohol (or remove it altogether) - 10 minute job
Replace the gasket with a proper Ford one. Careful to remove any oil in the grroove on the cover as it will prevent the new one seating properly.
Damn thing fixed for good now!
This post has been edited by keladrin: 26 October 2016 - 02:55 PM