Ah, well it does turn as you say, but it has a tendency to stick. There's quite a lot of grit floating about in there, I've oiled it with sewing machine oil but it hasn't freed it up much.
You're going to like this bit ...
In the bottom of the body of the distributor you should find one or more small drain holes.
They'll be right at the bottom to let excess oil and condensation OUT - and which will let stuff IN too.
The car is driving along .... distributor bob-weight plate spinning nicely at half engine speed, acting like a centrifugal air pump flinging the air inside outwards and upwards due to the bowl shape of the body ... and a steady little draight of air LEAVES the dizzy through the gap between the body and the dizzy cap. This means that all the time the engine is running, the dizzy is sucking a little air in the drain holes and sending it up the dizzy body, and out the cap gap. This is how the insides of a dizzy can get so filthy. And the air is not filtered in any way ... all that dust, grit, crap and grot that passes through the engine bay ... some of it is going in those holes ... just a tiny bit mind ... but perhaps for 20, 30, 40 or 50 years!
I would say a once-a-year clean out would be a good plan.
CharlesY