Definitely time for a re-build, Scott..

When the seals on my NS400 failed, the bike ran fine from cold but deteriorated rapidly as it warmed up.

The real kick in my case was that the crank had just been rebuilt - supposedly with fresh seals, so it took a while to work out where the problem lay. The situation was made worse by the fact that just about everything (engine/carbs/ignition/exhausts) had been altered in one way or another.

Hopefully, after a crank re-build, you'll be up and running again.

Regards

Mark
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If it ain't broke, fix it until it is.