Hello!
Fixed my odometer again today (last fix worked for only a few weeks then
quit). This looks like a permanant fix.
OK . . .
Step 1: remove speedo.
Step 2: remove back of speedo
Step 3: remove advance gears and rod - little gears above mileage wheels by
pulling out the shaft they are on. make sure gears don't fall off shaft.
Step 4: pull out shaft odometer wheels ride on by pulling on green gear -
remember what your mileage was!
Step 5: clean green gear and shaft end with alcohol, superglue two together
Step 6: between about 1/8" and 1/4" inch in from other end of shaft where
pot metal wheel rests take a fine thin saw or jeweler's file and score some
notches about 45 degrees off shaft. Idea is to raise metal in this area on
shaft (filing or cutting produces depressions, but lips of depressions are
actualy raised up) so shaft and gear is now a force fit - assuming your
gear is not broken (mine was not - just slid on shaft).
Step 7: reassemble. It's a bear getting the odometer wheels and advance
gears to line up right so you don't get a setting between numbers . . . .
Hopefully this will help somebody . . . it's not too detailed, but I hope
you understand what's going on. No need to take off speedo needle, etc. The
idea is to get some sort of "bite" between shaft and pot metal gear -
originally it was just a press fit between two smooth surfaces. My
speedometer had died at 120,000 miles and I advanced it to the more
appropriate 192,000 mile mark when I reassembled the odometer wheels onto
the shaft. Don't be a putz and try to subtract miles this way  - it's
really easy to ballpark vehicle mileage if you know what you are doing.
Plus, the Geheime Staatspolizei may well come after you . . . .