Here in the states they use various suction devices to create a vacuum that pulls the adhesive into the crack or chip in glass windshields. Might need a different adhesive for Lexan but the principle should be the same. Most of the auto glass replacement shops here have the device. Might try motorcycle shops too as most bike windscreens are either Lexan or polycarbonate.
Would think that most any auto restoration shop that deals in high end classic cars would be able to help with your leather issue.
