[scary driving]

You're in Brazil! There's like thousands of VW gurus over there (like more per sq mile than most places). Those guys might be able to help you out with your issue and might even find a buyer for your old exhaust. On the other hand, if you have a respectable tig welder, you might want to consider opening up to add absorbing material to the muffler. Although the "damage to valves" might be a stretch, you don't want that much heat accumulated on the engine. Overheating will be a problem with restrictions on the exhaust. If it's too restricted, it could be the equivalent of having a clogged catalytic converter.