Slick Service Bulletin SB3-08A
Before the 2010 Reno Air races, during testing, I found I had a timing issue with the engine. Over a period of a few hours the mag drop had gotten worse, and when the timing was checked it has drifted a bit. Once I was able to identify the timing was moving, I was very concerned. After a bit of homework, I found this service bulletin on the Slick 4300 series mags.
Below are the picturs of the parts that I had to replace inside the mags. Not only were the brushes worn per the service bulletin, but the bearings were shot, among other things. Many of the problems seem to be related to very high temperatures. These parts had about 200 hours on them since new, just for reference. I have now installed blast tubes on both mags to keep the temps down.