Dan - FYI.
I recently swapped the stock line out with a braided line. Here's the thread with the info and install advice from Blas and Velox.
Best way to access back of oil pressure gauge
Per Blas' post:
"Technically, the air pressure in that small
oil line is what registers on the gauge. The
oil does not necessarily ever make it to the instrument. (thought sometimes you can see some in the original plastic tube) If
oil actually made its way to the gauge, that tells you you have an air leak at the gauge fitting."