At work we use a weldwood contact cement that can be found at most hardware stores. Make sure it says for cloth/fabric/vinyl applications. You can also use 3M super weatherstrip adhesive for the mirror plug. It comes in a tube and works amazingly. Can probably be found at an autoparts store
Automotive Service Technology Instructor (34 year Fiat mechanic)
75 spider , 6 Lancia Scorpions, 2018 Abarth Spider, 500X wifes, 500L 3 82 Zagatos. 82 spider 34k original miles, 83 pininfarina, 8 fiat spider parts cars
son has 78 spider
you could use the weatherstrip adhesive on the boot too. The stuff works amazingly on anything. Especially plastic to vinyl. Just apply to the vinyl and the cap, not too thick or you might see "chunks" in the surface, let it set a bit then pull it on