Hi Tony, I would say the number one failure with Aeroshell 500 would be the carbon built up in and around the bearings, as you could clearly see in the pictures from Dirk's posts.
http://www.rcuniverse.com/forum/m_11492501/tm.htm In fact, he said that the bearing on the right was after he soaked it in the solvent tank and the crusty carbon is very difficult or impossible to clean off and has also coated the balls of the bearing.

Perhaps Dirk could chime in to tell us more...

Regards,
Barry