Interesting how things work . . . or doesn't work. I have Smiths gauges in my Cobra. No problems yet, but I did replace the plastic line running to the
oil-pressure gauge with an AN hose as a safety precaution. However, I do have SW's in the GT40. Keep in mind that Murphy's Law always applies. The only problem I've had is a failed Stewart Warner water-temp gauge (mechanical) in the GT40. And what a bear it was to replace. This is because you can't just replace the gauge, but the entire capillary tube-and-gauge assembly. Being a mid-engine car, this required dissassembly of the interior of the car.
