Posted for "Christopher Zavatson" <Christopher.Zavatson@udlp.com>:

About two years ago Matco also switched the material in their brake
discs.  I was looking for brake improvements when I came across this
news and so I switched discs.  I was impressed with the result.  I was
told the old material was precipitating carbon during use which was
acting as a lubricant.   New discs are marked with a D5 stamp, while old
disks have no marking.  Chris Zavatson
N91CZ
L360 std