Another thing I learned at the racetrack about engines and oil.  Cutting
open your filter each change can give you early warning of problems inside
the motor.  Race supply catalog and Cyber stores sell a tool to cut open
your canister oil filters with ease.
  Then you spread out some of the paper core and look closely at it to check
for metal filings and specs of worn interior parts.  I do it while the last
of my oil is dripping out, use a magnifying glass.  I once found some bronze
specs in my 928 filter core and knew I had a bottom bearing problem...We
saved that motor by replacing the #2/6 bearing the night before I went to
Laguna Seca, where for sure it would have blown..The bearing was spun,
sending bronze (or whatever alloy that is) into the oil system to be trapped
in the filter paper..
  Cheap way to see if anything is grinding any other thing off, inside your
engine...

  Don Hanson