Did you notice the blurb in AOPA EPILOT that Exxon has, and has been having,
deposits of grey crud in their bottles of oil, but they say it is just fine
and there is no need for them to replace it, or to pay to tear your engines
down...
Besides, there is a lot less of the crud in this months production run than
last months since they actually cleaned their pipes... Of course, they
don't know what it is, but they assure you that it is harmless and the oil
meets some spec or other...

Harrumph, this writer does not know of any spec for aircraft oil that allows
visible crud in the bottom of the bottles!

Denny