Jetmaniac, how could overfilling result in damage to the housing? the housing is one solid piece. Then there are 2 oil seals behind that (the housing). Overfilling causes excess grease to come out through these 2 seals exiting out the mid shaft exit. I do not see how using a HAND PUMP grease gun could cause any damage... excess oil will simply ooz out. If it could be damaged this easy Yamaha would have never put it on there. But they knew and made it so excess grease will simply exit.
http://216.37.204.203/yamaha_OEM/YamahaPWC.asp?Type=13&A=32&B=7
His post was dead on. If you pump in too much grease or pump it in too fast, you can unseat the seal which will allow grease to leak out. As he mentioned, it's a sealed bearing that doesn't need lubrication, but without grease to keep water away from it, corrossion will start.
A couple tricks I leaned are to grease it after a ride so the grease in the hose & housing will be warm, & do it with the engine running so the spinning shaft helps distribute it evenly inside the housing.
These pics are from a SHO inter shaft/housing, but it's the same desgin as a SJ. I had water pouring out of the housing at WOT, & when I pulled the motor forward to remove it, the coupler fell flat on the hull liner. The bearing was almost completely disintegrated. There was a big glob of grease in the hull under the housing, so I had obviously blown out the seal by overfilling or pumping too fast. Both the shaft & housing were marred up & had to be replaced, so it was a lot more expensive than just presssing in a new bearing & replacing seals.
