I have two JBL D120 reproductions built from original '70's D120F orange baskets/alnico magets that l would like to sell, but have a little problem - when I took them out of the speaker cabinet they have what looks like glue on the dust cap covers. For me to sell the speakers, I need to know what this is, what it means and if it's possible how or if it can be removed.
Picture attached
Thanks