It will definitely pay to replace the slotted screw with either a hex head or allen key version because 99% of the slotted ones fail and the slot strips out and your stuck with a real chit of a job to extract.  Be very observant of the order that the small filter sits (ie the direction) as its not obvious if you forget.

Do not be surprised if you find nothing as the filter is mainly about stopping large bits of stuff from heading to the top end.

So, this is what I found..... I assume the oil flow goes from the inside to the outside coz all the gunk I found was compacted on the upper inside.

Check these pics. The inside was about 1/3 plus filled with a mix of 'something'. I used brake cleaner to wash it all out onto this white kitchen towel. I ran a magnet over it and there appears to be zero steel. Thats got to be good. There is a few mega tiny pieces of thin black stuff that feels like bakelite. There are a couple of very small bits of very thin alloy. The larger mix of 'stuff' looks like it's a cats hairball. Using a jewellers eyeglass up close the bulk of it looks very much like fiberglass matting - Clear to beige strips of sort of matting material. I am wondering if this was from the filtering material form an oilfilter that never made it back to the filter??.  Into the mix is also what looks like two tiny bits of perhaps flat once compressed silastic. The other collection of black bits I have zero idea on.

Of note - the engine has never been apart and seems to run fine. So, in my sleepless hours tonight I will be worrying if I have caused any top end damage?? I am hoping that if the lower and wider 2/3's of the filter were not clogged enuf oil would have got through to do it's job???

Should I worry or just keep an eye on ot over time???? I usually like to adhere to 'if it aint broke, dont fix it'.  I am very keen for the collective opinion. Cheers, Oilleak.