Apologies if this comes 5-10 years too late for most of you...but better late than never!
Background/synopsis
The BA/Lantis/323 seems to suffer from excessive play in the wing mirrors, allowing them to rattle- and my 1994 Australian-spec model with "pre-Ford" mirrors is no exception. The excess play is apparently caused by looseness in the three external screws located on the (pre-Ford) mirror unit’s underside that cannot be removed by simple tightening. Apart from the audible annoyance, the rattle poses a safety hazard by making the mirror's image unstable.
Complexity
The fix is external, cheap, quick, simple and performed ‘in-situ’. It does not require any dismantling of either the doors or mirrors, however it does require some patience and dexterity.
Estimated completion time
10-15 minutes per mirror (when prepared and you know what you're doing)
Required tools and supplies
- Offset (right-angle) Philips PH1 Screwdriver (OS)
And/or - Ratcheting Offset (right-angle) Screwdriver (ROS) (preferred) with Philips PH1 bit. Note the head knob for finger tightening in the picture
- 3x 4mm x1mm thick plastic washers per mirror (min)
- Work mat/ground protection
- A low step/stool to sit on
- Some patience and dexterity
Steps
The procedure involves the shimming of the screws on the underside of the mirror to remove slack. repeat the steps below for each mirror to be fixed.
- Place a large tray, or rug or other soft material under the mirror, to prevent dropped parts bouncing away.
- For each of the three screws located on the underside of the (pre-Ford) mirror arm/base, one at a time:
- Carefully loosen and remove the screw. Due to the limited access space, use the OS/ROS.
To loosen the screw, carefully use the OS or ROS. Note due to the long handle, the OS/ROS can be difficult to align and exert a lot of force. Choking down on the handle will help with control and force limitation. If a screw appears stuck, do NOT force- proceed to the next screw. You may not need to fix all the screws to remove the play.
To remove screws once loose, it may be easiest to use the bit only from the ROS. The bit may be manipulated between two fingers or supported with e.g. the 'pinkie' of one hand and manipulated with the fingers of the other hand.
- Clean the screw and screw seat.
- Fit a washer to the screw.
- Reinsert and carefully tighten the screw. Use the same techniques as for removing the screw.
- Carefully loosen and remove the screw. Due to the limited access space, use the OS/ROS.
- Test the screws and mirror for play, retighten as necessary. If a screw shows play even after tightening consider fitting the screw with a second washer.
And there you are! The mirrors should be tight as new now.
(update)
Followup...
I found after a while the mirrors could start working loose again, especially if the folding mechanism is used. So I recommend checking, and retightening if necessary the screws after (say) a month or 500km, or if wobble is renoticed. Again be careful of overtightening, you are tightening using OS/ROS which can exert enormous torque compared to a normal screwdriver.
Hope this has been of assistance,
Pitrack_1
fold the mirror, squish the blu-tac, unfold mirror - done 
I was afraid of that. Since mine is a 1994 and the mirror design is different, I'll assume mine's a pre-Ford mirror. But thanks for raising the issue, it's something I was wondering about. I'll update my guide-post above.
Here's a better photo: