any ideas how this has happened as my garage are saying its fair wear and tear???

 

Ive had a few apart and never saw that.

 

Thank you for your comment. This in on a 12 year old car that has covered 107K. My warranty are refusing to pay out at the moment. I am a mechanic of 22 years in the army and also never come across this. Any ideas what could have caused it?

 

Any metal parts floating around? There is a magnet in there somewhere, cant remember where now.