I have a 1980 Sachs Prima with a 505 D1 Engine. I am having an exhaust leak at the exhaust flange. If I spray carb cleaner on the connection, the engine either stalls or revs up very fast. I had the exhaust pipe clamped real secure to the flange and then held up with springs attached to the head fins. Without the springs the flange drops down 1 mm. The bottom of the flange is pitted and can’t possibly seat properly. Has anyone put a copper sleeve around the exhaust flange and shoved it up to seal the gap? It may better than Permatex 81878 Ultra Copper Gasket Maker. I would appreciate any other suggestions for sealing the gap.