To what degree of accuracy do you want to measure and over what length? There are many solutions here in Europe for machine vision inspection systems, you can check with the machine vision association for specific vendors, see http://www.bmva.ac.uk/
However, its best to put your money into...
If commercially, available joints are not quite the ticket, it’s relatively easy to make your own rotary vacuum seal.
A labyrinthine seal should provide the features you are seeking. The labyrinthine seal essentially a vacuum cup with a plug mounted on the same shaft, the plug fits within the...