[ulfilias]

Had another go at this today. The discs turned up and I fitted them to both sides, checked the pads were even and balanced.

No joy. The left still runs and runs. I popped the left side off again and tried the old motor and same thing. I had a C clip in the new motor parts, but never bothered changing it. It goes on the piston side around the large star drive slot. I took the old one off, cleaned things, checked that things were freely moving with a star drive and, yes the internal (worm screw?) seems to work fine. I wound it in and checked the caliper and made sure that was moving reasonably and cleaned things a bit too.
I put it back together but left the wheel off and ran the test.....It seems like the motor isn't engaging and turning the internal drive....But i can't for the life of me figure out quite how / why!

Both the new and old motor have the wobble drive thing, which seems like some form of clutch and allows the Star drive to engage and disengage and it just doesn't seem to do it in practice.

It's all a bit odd and i'm not entirely sure quite what to do next....I guess there is the option of a whole new caliper perhaps....But it seems a lot of hassle and expense for something that in all essence appears to work, but just doesn't!