My NA starter had the same intermittent failure to engage the flywheel. I stupidly thought the problem was the starter and bought a re-built unit. It didn't help the problem, and after the bad flywheel was replaced, the re-built still failed to engage. Then it was necessary to purchase a Denso, which works fine. Big bucks, and feeling that the original starter was probably OK. I had been advised to avoid re-built, but did not listen to advice on discussion boards.
