That dustoff stuff is probably
hydro-bromo-choloro-fluoro-metzo-piano-carbons, and does a lot of damage
to the Bozone slayer.
I'd think some CLR or dilute muriatic acid sprayed into the system, to
dissolve the calcium scale. But, I'm probably out inspace.
Christopher A. Young
Learn more about Jesus
Consider trying to blow the tubes/hub clear with a can of compressed
air. Office supply stores (Staples, Office Depot etc) sell them for
cleaning computers, printers, etc.