I've had an AutoMeter C-2 model oil pressure gauge on my ride for 8-10 yrs(temp on the left, fuel in the center) now with no trouble. It's not a mechanical however, it uses an adapter at the point where the OEM pickup was. I found it easier to work with and mounted the gauge on the handlebar. That would be impossible with tubing, plus tubing leaves more room for vibration problems somewhere down the road. Here's an old picture of the front of the bike, I no longer have those particular leathers.
