The first thing I check is for a clog in the tubing when the DC seems
to bog in performance. Many times I find sticks blocking the way.
The felt bags get a 1/2" layer of fine sawdust on them, and I knock
that off but never wash them (per manufacturer's recommendations).
Over time, flex-type tubing will need replacing as more pin holes
appear. Another improvement is rewiring the DC for 220v for better
starts, smoother cooler running, and less power consumption.