TT belts...clean before ??

I have a SME 20/2. I can hear a slight increase in sound quality when I install a new belt. After a year or two, the belts become cracked and brittle. Not completely, but somewhat.

Question: The new rubber belt I just recieved has what looks like a grey powdery residue on the black rubber. Some kind of mold release compound? Should I remove this? And with what? Alcohol? Will that breakdown the rubber?

I also usually clean the motor spindle with contact cleaner to remove any debris/residue. Good idea?
The powder is there to improve traction; I would leave it on. VPI belts are powdered, and it makes sense to repowder them every few years as the powder wears off. Just put them in a baggy with powder and shake.

Many flexible plastic and rubber products have chemical softeners in them to keep them flexible for years. Many commonly available cleansers have agents that remove such softeners, causing the item to become brittle before their time. This is why we shouldn't clean a vinyl car seat or dashboard with common "household cleansers," or else the vinyl will crack in less than a year. Same with rubber belts.
The powder is a preservative for the rubber to keep it from drying in storage. DO NOT use alchohol that will shorten its life. Simple Green works real good on rubber parts