My issue with mechanical is that little plastic line of pressurized oil, and where it runs to/by. They are fine until they're not, at which point you have pressurized oil dripping and/or spraying, most likely into the cabin, usually behind the dash onto electrical components which tend to get hot. I think it would be wise to hard-mount a mechanical gauge directly to the engine, and use electrical gauges for going into the cabin. Kind of a best of both situation. Use the in-cabin electrical as a heads-up, and under hood mechanical for verification. I'll likely take this route.
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When my dads Corvette was taken apart, we figured out that the mechanical oil gauge had been leaking onto the radio, for who knows how long, which explained why the radio was getting worse with time. Had that car not been taken apart, it would have likely only been a matter of time and heat before a fire. C3 gauges are directly above the radio.
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