What do you mean "starting to slip?" Can you feel it's speed drop but the engine is still revved up? Do you hear a slight grinding noise?
Wait, let's go back to your original problem. The pump locked up, right?
Did this happen while running? If yes, your pto is very likely stripped. The pto is the hub looking thing on the rear of the engine. It is made of softer material than the drive shaft. I sucked some seaweed in mine (I think) and it destroyed the wear ring. After this, mine would slip out and free spin. Both of the rubber spacers were gone, too.. When I pulled the pto, it only had splines at the rear edge. The rest was gone. So I replace both and bought new bumper spacers.
This thing is a bear to remove, so first, pull the pump again. Remove the seat and the air baffles. remove the grey cover over the pto. Pull the drive shaft. Get a small camera of use the one in your cell, if you have one. Take a few pics looking into the hole on the pto. Try different angles so you can see the splines well. Look at the drive shaft splines while you have it out. Clean it up well and see if you can see wear marks on it real close to the top (outermost contact point) of each spline. From this you can decide if it needs to come off.
If it does, get that impeller tool out and the longest breaker bar you can find. If it's too stripped you may need a chain wrench. If you're sure it is shot, a pipe wrench will work.
Follow this thread:
http://www.seadooforum.com/showthread.php?53078-SBT-engine-swap&highlight=flywheel
Some pics for reference, my drive shaft and PTO:
Hope this helped
Kevin
