Found in oil pan

[promsi1960]

So I was doing the process of changing the chain guides on my 1998 Porsche Boxster and found the Chain tensioner unit to look like the picture - the back guide was completely missing and the metal clip under it has significant groove - so i will be ordering one of those today from Pelican. My question is when I dropped the oil pan to find any chunks of plastic or metal... I found these black circular pieces in the oil pan. Any idea what they came from?

Another question has to do with the sprocket from my older Boxster. In watching Jake Raby's videos he says I should replace it with the newer style... Is this really necessary? is there something that goes wrong with these sprockets?

Thanks in advance - I am new to tearing into this car and appreciate all the help I have found on this forum and many videos