A little more work this afternoon, we modified the as bought passenger side window retainer mechanism
Cleaned up the regulator guide and replaced the disintegrated nylon retainers with BMW units from ebay with bolts through them. I've used nyloc nuts on the boltd and they have a steel washer with a fibre washer against the window glass under the nut at the back. Seems to work ON and doesn't foul anything.
Regards,
Tote