yes evan give penality, dexcool is the way to go, did you see in your manual if The Rotax 5 year rubber replacement covers all fuel, oil and coolant lines as been performed,
some people inspect the hose from the outside and looks great, like we did on one of my aircraft, we have the same issue as you just mention, so we remove the radiator, and find inside of them smal ruber piece, the came from the coolant interior hose are dissetagrating them self, but before this, with flush the coolant, do some oil change, and else, before we came to this... if you can inspect your hose interior, and inspect the interior of the rad, on my side, i have to replace them, they was cloged....
