We are selective on when we use Prist. We usually do not use additional Prist on fueling a return flight, as we know there is still some in the fuel that is left. We want to be very careful not to over-Prist. We know you don’t want to store a plane for extended periods with Prist or probably alcohol for that matter. This is our first winter with the 421 – it never seemed to cause an issue in our 58 Baron. And yes, that is the correct mixture. It is clearly marked on the canisters.