Having fixed the interior mirror that was vibrating out of position, next to do is the exterior mirrors. Off-side vibrates out of place, near-side is very stiff, hard to adjust, both looking tired. Both have the moving body on a round boss pressed into the mount - not nice, hard to get at rear mounting screw. Took off the near-side glass, and unscrewed the base - to find 1 front screw hole, and 3 at the back! Spacings are 100, 110, 115mm. Took the mount down to my local Retro-Spares shop - identical to 70s Ford Falcon(XA,XB etc), plenty of stock. These have the mirror body screw into the base, but will need vise-grips to apply any torque. 2 please. The off-side base was retained with M5 philips head screws, into what looked like riv-nuts, which needed a bit of thread cleaning. Near-side base had self tappers. After getting the new ones fitted I looked why the old units were stiff and/or loose - small struggle to pull the circlip holding the glass in place. OK, could have tightened out the looseness, as there is a plate with 2 screws bearing on the back of the pivot ball. The near-side unit was very rusty inside , so it must have spent a long time out in the weather, which it wont do anymore.
So, now all the mirrors will be easy to move, and will stay where I put them.