Stator cracks are post injection stress relief/shrinkage cracks and will not cause any issues at all. They are not caused by operational stress, but by stresses caused by injection moulding plastic over the top of the steel laminated core. These cracks appear soon after they are first used, as they are the result of stress relief.
In the early days (F&P the manufacturer) went to great lengths to control these cracks, but once it became apparent that they did not grow or cause any issues, less crack relief holes were implemented in recent design variants.
The picture below shows an old 100 stator, despite it being 20 years old it looks like new (we have cleaned it). You can see a lot of crack control holes, these help to prevent shrinkage cracking. The picture above is an almost new 60R stator and you can see a crack and only a few crack control holes. The more material you remove the less cracks you have but the weaker it is. This might sound a little odd, but it is the case as you can clearly see.
Some clients seem to think the sky has fallen in when they see a crack like this. Just leave it alone, do not try to fill it or glue it, it is fine. If you ever get a failed stator due to a crack (from operational stress) we will send you a new one for free. If you drop it onto a concrete floor yes it will be cracked and ruined - we do not cover this, try your insurance company.
Rotors on the other hand should have no visible cracks in the plastic body. Hairline cracks in the magnets are fine and are no issue.