I've done a search and come up with lots of posts with problems with rear wiper and wash but dont seem to find an answer for mine.
Rear wiper works fine.
I have water exiting the one way valve to the motor.
I've checked the jets aren't blocked.
so it appears the blockage is through the motor itself?
Is that a common problem with a fix or is it a new wiper motor req?

Yes, it's a common problem.

Take it apart and use plenty of thin wire or compressed air to clear out the blockage.

No need to replace the motor.

Have a look in the Wiki, there should be some guidance in there.

Mike

Try use powerwash with a good blast, it's work for mine one
Had similar problem😁😁😁😁