I think there's an outside chance that the unknown adhesive Dave Krall
is looking for may be gutta-percha. If it is, your local dentist may
be able to help you with softening or dissolving reagents. Its use in
the dental industry, however, is more of a root-canal "filler" than an
adhesive. Ref. https://en.wikipedia.org/wiki/Gutta-percha 

John Grant

 [ At https://www.merriam-webster.com/dictionary/gutta-percha 
 [ "Medical Definition of gutta-percha: a tough plastic substance from
 [ the latex of several Malaysian trees (genera Payena and Palaquium)
 [ of the sapodilla family (Sapotaceae) that resembles rubber but
 [ contains more resin and is used in dentistry especially as a
 [ permanent filling in root canals."
 [
 [ At http://plastiquarian.com/?page_id=14211 
 [ "Gutta percha is very difficult to find today in anything other than
 [ antiques. A recent television programme about the history of golf
 [ found its researchers scouring the country to find some virgin
 [ material. One small sealed tin was eventually found in Hertfordshire
 [ and, when opened, it revealed a slab of pale cream pure gutta percha
 [ which had not seen the light of day for many decades. After filming
 [ the tin was re-sealed for posterity."
 [
 [ -- Robbie