I have had coolant leakage problems in the past. Once was incorrect water passage O-ring installed between clutch case and center case. So from that time on after rebuild I would pressurize the motor coolant system 15-20pis, then check for leaks, with soapy water. My last rebuild I had gas passing around the head to cases, very little but leaking. After trying a other new head gasket which did not help, I used Permatex Copper Spray-A-Gasket which has stopped the leakage, now the cooling system can hold its 15psi for 24hrs.
Mars
Husaberg FC550 2001 Original owner.