Thanks very much for the info ra.ra, I'm hoping that's what this is! Here is a more closeup photo. There does appear to be a couple of larger globs of this stuff here and there, hoping that doesn't make a difference - just want to be sure I can safely apply the AR vintage sealant stuff as I know these speakers haven't been touched in maybe 15-20 years. I also had a question about the voice coils - when I press down gently and evenly around the woofer, I hear some intermittent rubbing which concerns me. I pulled this cab apart before I even had the chance to test them. I did however do an ohm test and I'm getting a steady reading of 3.5 ohms on the woofer which I believe would indicate the voice coil is intact, but any suggestions about the rubbing? Thanks!