Does this happens when you ride or just friends? If it doesn't happen for you, then you probably do not need to replace the exhaust gaskets.
Unfortuneatly the x2 is very bad about ingesting water. It usually comes in through the intake, not the exhaust, but water through the intake doesn't usually wait until you shut it off. However, it can get into the crank and let the ski start until you shut it off and sit, because it can start easier with water in it when it is hot than when it is cold.
For an intake related water ingestion problem...
- spend some time sealing the engine compartment
- make sure all holes that wires go through are sealed; if not, add silicone
- make sure you stock siphon bilge is properly mounted so water doesn't roll back through it.
- check for leaks in the cooling system
- install a bilge. A single rule 500 is acceptible for the lake. Duel 500s for the surf.
- make sure you have a good hood seal.
- duck tape the hood (at least the back corners where the most comes in, but preferably everywhere) until your friend learns to ride better
- go back to the stock style airbox that protects the intake
For exhaust related problem...
- replace all of the gaskets touching the exhaust manifold (though this isnt the problem of this happens to only new riders)
- brap the ski a couple times on the way in to clear the water box some right before shutting it off.
- install a flow restrictor (like jetworks) that reduces or stops the water into the exhaust at idle
- dismount the ski to the left, so any water in the pipe rolls away from the motor rather the towards it.
- put your ski on a beach stand and rev the motor when you get in to clear the exhaust of water
Check your oil...
- get a glass cup with a lid (empty spagitti sauce jar works good) that you can throw away
- mix oil and water in the jar about 10:1
- shake vigorously.
The oil should bead up immediately (10 seconds) like cooking oil (if you are not sure what I mean, make a batch of cooking oil as a test sample, it should be almost that fast).
If it doesn't separate like cooking oil, change to a better oil.
I we running generic oils but they mixed with water, so I switched and my boat ran better.