My two brothers and I have always used the Poston's gauge (the small one with the braided line that you can leave under the hood or stick out in front of the windshield). For some time now Ive had a Autometer gauge attached to a homemade bracket and sits at lip of hood in front of windshield (its bigger and lighted, so I can actually see it).
We have had no trouble from either gauges. Ive always recommended the Poston's gauge for a quick setup.
Is it the gauge itself that is leaking, or is it from where the fitting on the line screws to the gauge?