One of the best reducers that will thin almost anything is MEK (Methyl Ethyl Ketone) It will strip paint off walls, remove sticky bonding agents, ect... As a guitar finisher we use this to reduce our Catalyzed Polyurethane (Lacquer) that we use to build an incredible durable finish on high-end guitars and mandolins. Pure Acetone and mineral spirits like Naptha are pretty good as well for certain applications but for a glue such as Goop this may be the way to go. Never used Goop myself I have no need and would just rather buy Flexament for the few uses I do use it for. Like the other stuff if you start to get a headache or see stars or start laughing uncontrollably or _______ you will start loosing braincells. Oh ya, alot of these burn really well too!