FlyingForFun think you got that the wrong way round, The heads are watercooled and the cylinders are air cooled. The Rotax 912/914 is a very reliable engine if maintained correctly for some strange reason there are people out there who still cant read the maintenance manual.
As for the Centurion, yes the TBR (time between replacement) still stands at 1000 hours but the manufacturer says that the life time should go up to 2400Hrs. See
Here.