4.5v Motor Variations

[BrickWild]

Have you noticed that the 4.5v Technic motor first produced in 1977 has some variations?

Here, the one from 1032 Technic II set from 1985 has a 'hollow' spindle and the one from 8700 has an 'solid' spindle.

In my opinion, the 'solid' spindle has obvious advantages over the 'hollow' one.

[Jundis]

Looks more like improved and/or more cost efficient production to me. I think booth spindels use a outer plastic sheath and an inner metal core. The older one on the left have to be manufactured with a blind hole, which is slightly more labour intensive than to drill through. But its just a guess...