Try an oill based product like white spirit or parrafin, it will not affect glassfibre but as the glue is oil based, it will eventually turn it rubbery again and will make it easy to remove. Leave it to soak if it's old and hard as it will take time. If it's in a place where you can't make the fluid pool around the glue, soak a rag in fliud and drape it or bunch it up over the glue area and leave it... it will soften the glue eventually. Petrol works better but it's smelly and highly flammable of course but it works...... Ive done it before.