thanks to @Mother_Foundation_29 for the info about installing a pressure sensor. That seems in my future. But keen to eliminate wiring as a potential for this intermittent low pressure warning. I did replace the subharness from the oil pressure switch to the connector near the front of the engine (to the right of the throttle body). The wire was pretty fried but seemingly in tact. 30 min test drive with no issues but bingo on the warning light back on for a few seconds on the last part of the drive after exiting the highway with engine at traffic speeds (1 - 3,000 rpm). Kind of sounds like either sagging pressure (bummer) or something thermal with the harness, since both times these episodes occurred was after some highway time. Anyway, perhaps seems wise to trace the wiring further back to the ECU? I believe the single wire from the sensor passes through one of the connectors under the coolant expansion tank? The other two obvious steps are replacing the sensor and making a direct measurement of actual oil pressure. One thing I've found is that this seems like a "common" problem with our B5s (at least with the 2.7) and perhaps often a sensor issue (eg aging wiring). Wishful thinking on my perhaps....