Last summer, on a beautiful summer days drive, my car quit...early '67 250 SL. Had it towed home and the fuel pump (tall version) was not running. Not having anything to lose, I removed the pump and then started dismantling the motor on the bench. What a mess of filth after 42 years. I blew it out, cleaned it out with carb and electrical cleaner, in general, spiffed it all up inside. The brushes were worn, but still making contact. Reassembled, attached a 12V external source and I was in business again.
Last Saturday, 900 miles later, things were getting funny on the throttle while on the freeway. I exited as soon as I could and the car died. Pump out again. Towed home, removed pump, took a quick look and decided the brushes were probably too worn. Took it to a local electric motor shop. He confirmed my brush theory, custom fit a set of new brushes and said all is well. $78. I reinstalled a nicely humming pump and went for a spin. While my car has always been a pleasure to drive and is very smooth, it seemed to hit a new level of smoothness and responsiveness. With the pump operating at full capacity, the injection pump is now most likely getting a consistent flow of fuel at full volume allowing it to operate even more efficiently, while before, without the new brushes, it may have been flowing at a slightly diminished capacity.