This part has a good pump but the electric motor portion works intermittently. When it decides not to work you can knock on it with a wrench and it will work again.
Is it easy to take these apart and repair or would you say this part is junk and should be scrapped?
Easy to work on. Save the old O-rings to match-up at your local store or NAPA, and watch for the two little ball bearings used as check valves. Intermittent is likely old brushes or corroded commutator, but may be deeper. Well-stocked hardware stores can match-up for new brushes, or check at (or drop the motor at) an electrical/motor repair shop for a once-over, if that's not your thing. The same pumps were used by every brand for decades. I got a nice pump at the wreckers for $15 that was identical to my Ford in a 1990-ish Dodge K-car.