If you're getting that "slipping clutch" feeling out of the hole and you didn't before, it's time to go through it. 

Check out the berkeley and american turbine website...one of them has rebuilding instructions with photos so you can familiarize yourself with it before you dive in. 

Most problems are due to the leading edges of the impeller getting beat up and/or the wear ring/impeller pilot getting worn and opening up the wear ring clearance. 

The basic rebuild is pretty simple, but after tearing into my first one a couple years ago, I found of lot of issues with what seems to be accepted as a quality rebuild, and chose to do things a little differently. 

For a stockish application, simply changing the parts and shimming the new or reconditioned impeller for proper wear ring shoulder clearance will be fine.  For performance applications if you want it to be as good as it can get, some machine work/alignment/balancing is in order.

True story. That. Pumps will, at full throttle, boat not moving, suck stuff off of the bottom from 4 to 5 feet! If you are in reverse, the reverse water blows stuff up right under the intake! I make a practice of never hammering the throttle from a dead stop unless the water is about 10 feet deep, but then again, I don't like throwing money away! We had a customer that always beach launched his ride, and would warm it up on the trailer by revving his engine, he killed his new pump in 2 months! TIMINATOR