In the process of selling my 02 519. Had the diagnostics pulled and it has 299 hours and no faults ever thrown.
They pulled the compression as well and were
90, 110,110,100,100,100.

The tech said all was good, but I�ve always heard the 10% rule, so that 90 cylinder concerned me a bit.

The motor has never gave a moment�s trouble. Anyone with any input on this ?

Have you ran Yamaha Ring free or de-carboned motor. Sometimes decarboning the motor will bring compression up & help get them back to 10% differences. Worth a try. If not it's a good time to rebuild it for you or anyone looking for a good rebuild candidate.

Yes the motor has had ring free ran in it from birth. How do you decarb one ?

I run Seafoam in my fuel about every 4th tank. It doesn't carbon up when I do. Ring free keeps them pretty clean & yours is probably pretty clean. It was just a question if you didn't run it. If you have a remote tank you can hook up put 3 gallons in & put double dose (see instructions on can)of Seafoam in it. Start motor, let it run for 10 minutes minutes. Kill & let it set 1 hr. Crank it up & see if it blows black goop out the prop. If not then its clean. You can use whatever Yamaha decarbonizing additive Yamaha calls for. Not the Ring free but the one for heavy decarbonizing. I don't know what Yamaha calls it.
Was just saying carbon is a 2 strokes worst enemy & CAN cause loss of compression amongst other issues. Ask the service that ran your diagnostics about decarbonizing it or if they think it needs it.

Thanks for the info ! Ended up having the head gasket blown in that one cylinder.