Sounds as though the mileage is OK.....
If it is an '89 it should have a two-pin set of clocks which are easy to come by on ebay etc. You will need to take the steering wheel off, and then remove the dash facia, switches, radio and heater controls to get to all the switches.
Sounds complicated but it really isn't if you take your time and watch what you are doing. Once you have got to the clocks you need to get your hand around the back to disconnect (or push back in- may be the problem!) the speedo drive and the vacuum pipe. Then just tilt the clocks forward and carefully take them out, and make sure you don't damage the blue flexi-circuit board.
All in all about 30 mins work with a good cordless screwdriver- I managed it first time without breaking anything- a bit of a record for me!
Once the clocks are out they can be carefully taken apart.