The Cessna Service Bulletin SEB95-3 describes damage to the flap support arms from the edges of the rollers cutting into them as the flap rollers rotate. Cessna fixed the roller end wear problem on the forward roller locations by installing a thin stainless steel wear washer between the roller and the flexible flap arms.
The aft roller location is more difficult as it is up in the flap structure and is rigid. The flap support arms will not flex open for the addition of wear washers like the forward roller location. The aft long roller position has the same wear problem as the forward roller locations. Since there is not room to install a wear washer with the existing roller, McFarlane designed a roller slightly shorter in length that allows room for wear washers on each end of the roller. The wear washers are designed with a step in them to make them an assembly that is easier to install.
Note that the upgrades do not change the aft narrow roller and shims/spacers that control the flap lateral end play. P/N MCSK100 only replaces the unprotected long aft roller(s) on each flap. Replacing the flap arms that have excessive wear is very expensive and time consuming. MCSK100 stops any further flap support arm wear.
