O300D Aluminum in Oil

Well had my 1st oil change today. Have owned the 1964 172E for just 25
hours. When the filter was cut open we found a few small slivers of
Aluminum.

When I bought the plane the pre-buy inspection was a complete annual and the
mechanic didn't mention any "aluminum in the oil" so apparrantly this just
started.

What is the likely source of this aluminum? The mechanic suggested that I
fly for 10 hours and change the oil again to see if the problem goes away.

Anyone seen a situation where aluminum in the oil was a one time thing?

signed
"Not having a good day"