Finally got to the top of the *things to do* list:-)

With the door fully closed, taking out the main drive roller is simple.
The slats are linked to the roller by 4 curved aluminium connectors,
each secured by a pivot pin. The pins are held by two nylon rings which
form a surface for the slats to *roll up on*. The rings are retained by
large pop rivets fitted in a longitudinal slot in the drive roller.

I found it was possible to slide the rivets along to gain clearance and
separate the pins from the nylon rings which released the slats. Either
end of the drive roll is an octagonal flange slotted into a welded cup
and retained by 3 grub screws.

With the screws removed and the motor disconnected the drive roll can be
lifted out of the cups and manoeuvred clear of the support brackets for
examination. Best done by 2 people.

The tubular motor is supported at the supply end by a plastic moulding
and at the drive end by an aluminium casting which engages with internal
flanges in the drive roll. 2 pop rivets are used to fix the casting to
the roll. Once the rivets are drilled out, the motor and casting can be
withdrawn.

The motor drive is by a plastic spline secured inside the ally casting
with a grub screw and a retaining plate.

In my case, the epicyclic gearbox was smashed thus removing both
mechanical and electrical means of opening the door!
--
Tim Lamb