Tire conditioner on bias plies - help!

[StealthBird]

I'm hoping someone has the answer on this. The last couple weeks, the weather broke around here (in the 50-60 degree range. I have Firestone F70-15 redlines from Coker, I've had them for over 7 years, no problems.

However, this year, I took the car out, parked it, then got out to see if everything was level, etc. The tires (inner and outer sidewalls) had a chalky coating all over them, which wasn't there when I left the garage. I used Armor All Cleaner, and it removed the chalky texture (with a little rubbing). A week later, tires look fine, I take the car out, and the same thing happens, only not as severe. A week later, still some blotches of white chalky marks. I'm assuming this is coming OUT of the rubber?

So my question is, have any of you had this happen on Firestones? If so, what tire conditioner do you use to stop this from happening?

Over the years, I've tried No Touch, Formula 2001, and Armor All Cleaner (not the shiny stuff). As of this year, I'm just using the Armor All Cleaner. I know the chalkiness problem has happened to me in prior years, but I can't remember what product I used to fix the problem.

I'm a Firebird guy, so go easy on me.