I have an 84 300D Turbo that had the same problem. I went to the Steve Brotherton post, printed it out and then commenced to taking out the odometer. I fixed it once (or thought I did) but after about 250 miles, it started to make a click/popping noise from the speedo area. NOT GOOD! So I disconnected speedo cable until I could drive 80+ miles home. I worked on it this past weekend and the advice I would have for you would be this:

Follow the instructions that Steve Brotherton posted but as an additional comment, be absolutely sure that you get the brass "pressed on" bushing on the other end of the shaft from the brass odometer gear fitted snugly against the stamped metal frame and that the brass odometer gear turns fairly easily... and then test it by getting a drill bitt or some type of drill fitting that you can insert in the odometer to turn it and make sure the whole contraption works. The thing you have to remember is that if you have ANY binding on the gears, the worm gears leading up to the brass odometer gear are all plastic which is now 17+ years old so it is getting hard and brittle. I had to do some impromptu engineering to get the broken worm gear back in place after my initial repair. I have gotten this repair successfully completed now and it is working flawlessly. I would also caution that you need to be very sure which length of the shaft fits within the pot metal gear for the odometer (which drives the tenths on the trip odometer; thus why when you roll to the .9, the extra burden on the shaft/potmetal fitting is too much and it all stops right there!) before you put any punchmarks in the metal shaft.. that may be what caused my binding problem with fix #1 and so I sanded down the overlap. When I fixed it again, I noted that the brass pressed on fitting on the other end had slop in it and as a result the gear backed out past the worm gear ever so slightly which was enough to break part of the worm gear Test it well before putting it all back in there but once done, you will be really happy and able to really check that mileage!!