Welcome, Mike. Glad you posted and really glad the woofer is working out for you (in case anyone misunderstood, I gave him a good one to use in place of one that was "upgraded" to a Rat Shack driver or some such thing). I also encouraged him to refoam the other driver (pictured).
As far as the dust cap goes, I've had good luck spraying those cloth ones (cloth IIRC) with a water mister then pulling the damp cap out with a vacuum. Easy on the mist and approach slowly with the hose.