In my RV-12 / 912 ULS, the first sign of a possible sinking float is a faint smell of fuel in the cockpit during climb-out. The engine runs fine otherwise. In my experience, ROTAX has not honored any of their replacement floats once they replace the first failed set. It seems they do not warranty the factory-defective replacement floats that are installed to replace the original factory-defective floats. Very disappointing.
