I have an ageing DC-18 & it was loosing suction due to a widening hole in the hose to the power-head.
I fixed it by slipping a piece of 2 inch bicycle tube over it. It had to be long enough to cover a cpl inches above & below the hole to get decent friction & a few smaller zip ties on it. It wasn't easy getting it on, bunching it up like a wet sock at times & spending more time on it than I wanted but patience paid off.
It worked beautifully & restored suction to 100%, it was like it was new again.
Please share as this was a relatively easy fix.