I have a 1967 Camaro. I put in a Stewart Warner mach. Oil Guage 20 years ago It still works great and I have never had a problem with it.
It still has the original nylon / plastic line too.
There is always oil in the line, once in a while it gets a few bubbles but it never jumps around, just goes up and down smoothly with the RPM's [img]http://www.stovebolt.com/bboard/ubb/biggrin.gif[/img]

Kelly
1951 Chevy 3100
1967 RS/SS Camaro