As a result of the comments received in respect to my earlier post on this I decided to have a look under the plate to see what the filter looks like following my attempt to clean it. I was also concerned that when I banged the cover bits were dropping out from behind the plate. The bits seemed to be bits of carbon / the remains of burnt old oil. In fact I ended up looking under the plates that were fitted in three rocker covers that I had in my garage. One I had attempted to clean by just flushing it with white spirits. The other two I had initially flushed them but followed this by attempting to burn the contents out.
I can’t say how many miles they have been on the various cars but club members who know me and my cars will already know that at least one of my cars has covered over 300,000 miles.
The outcome is I certainly recommend that you have a look under the plate if you have a high mileage car because I was shocked to see what was left under there. Only one looked anything like what I would consider as being acceptable. See the attached photographs.
My question for the experts is why was the filter there and do I need to replace it?