My searches are not going too well.
Mine decided to flip past 9K after some spirited driving last week. It came back alive, then died.. then fluttered all over the place.
Since then, I was able to get it working perfectly by pressing on the top-right section of the cluster while driving.. until I hit a bump and it went haywire again.
So on the weekend I pulled it out and did pretty much what is described here. I filed the plug (all contacts) so that they were shiny, then got contact cleaner and went over all the tracks in the sockets on the back. Initially I had it loose and started the car, fiddled with the wires and couldn't make it play up.
After the cleaning, I put it back in (not screwed in) and turned the car on and off about 5 times. I revved it past 5K (the point at which it used to fall down to 9+) and it was fine. Put it back in, put the dash all back together, tested in the driveway while pushing all over the cluster and banging the dash... it was fine.
Went for a drive, and it failed. =-/
I'm at a loss, and I can't find any guide on how to replace the tacho with another from a used cluster, but I assume it's possible? Help on the topic would be appreciated!