Hi Mick. It could have an engine problem, but I would inspect the starter drive carefully, I have see a lot of Non Genuine drives that are very brittle and shatter as and when they feel like it, ( I would think that most components would now be non genunine as Lucas don't manufacture new parts now ) I can't really see a genuine Lucas pinion shattering or even breaking 3 teeth off unless the gearbox is badly out of line and the teeth are not meshing up correctly and then it would sound terrible when it was cranking.
What was wrong with the original Starter motor. ??