Need Help..How to fix Duster Ralley Mirror Assembly?

If it's a painted mirror, you'll probably have to re-paint it after the 1st part of this tirade.

To remove the glass soak the mirror in Gasoline, carb cleaner, etc. Something that will loosen the glue that holds the glass in.

Remove the spring steel bracket (Originally riveted with die-cast studs), then slide the mirror mount plate all the way back in the housing.
Using a small slide hammer and 2-pronged hook, along with a friend to hold the mirror body, CAREFULLY hook the backside of the ball and give it a couple of slight taps to dislodge it.

Once the ball is out, remove the plate and smooth the backside where the old rivets were.
Using the mirror mount as a guide, drill 2 holes, about 3/16" in diameter, in the general area of where the old rivets were, pass the ball back through the mirror mount and affix the spring plate back to the mirror mount with ALUMINUM pop rivets.
Make sure the ball is rustfree and well-lubed with a light grease.

Re-affix the glass with a proper glass adhesive or high grade silicone.

This method is a bit more work, but the repair will last and it's easy to fix if does screw up again.

Mark.