Hi,
the video gives you a step by step tutorial how to open and how to close the fully mechanical speedometer of a Porsche 944 mark 1. In the actual case, a shaft was blocked by corrosion, leading to a gear turning on the shaft. Some oil helped to bring the shaft in operation and the gear was glued on the shaft.
http://www.youtube.com/watch?v=aIGVe96yzN4
The video has a German soundtrack, but English subtitles are available at YouTube. If you don't see them by default, watch the video directly at YouTube and press the subtitle button below the frame.
Enjoy it,
Jürgen