Hi Joel, I had similar problem with chained notes starting to repeat.
My piano was properly rebuilt.  What I found that made a difference
is to use very thin green dental "GUM" brand brushes from the drug
store to keep tracker bar ports clean in addition to vacuuming.

There's a build-up that occurs gradually even though you vacuum
regularly.  These little plastic brushes loosen this build-up for
the vacuum to take away.  Each brush has a handle at end so they
can't accidentally get stuck or too far down in the port.

I hope this helps you as it did me.  I brush every other month.
You're welcome to contact me via Email if you wish.

Mark Labancz