If you just got it back from the service its possible a Hose was just not connected tightly enough, yes you are correct. Or possibly your carbon ring. I would first check all connections to see what is leaking. If your at home then simply connect to your water hose start engine then turn on water. Look into engine compartment and see if anything is leaking. If you cannot find the problem turn off water then engine. Then next time you can put the ski in the water leave it on the trailer with the seat off and the ski strapped down to your trailer securely turn it on with the seat off and once again see if you see whats leaking. make sure plugs are in. Good luck