YES the magnet POLARITY does make a difference.
I put the original magnet slider into the new blind, and manual gear shift works again.
The part from China was labelled 8699465 on the pack but also says S40 and C70 on the pack. The advert said C30, S40, C70.
The slider part with a magnet is marked POM2 and the original POM3.
Placing the two slider magnet faces together I found they attracted. i.e. if the face is North on my old one then it's South on the new one. I had expected them to repel, i.e. both be North faces.
