There seemed to be enough oil in the van this morning. I took it to Jiffy Lube and they said it might be a half-quart low (and they topped it off), but that is not enough to cause the wild variance on the gauge readings. They said they couldn't do anything about the oil pressure sensor, so I contacted my regular mechanic, and he told me to bring it by and he'll have a look. I left it with him this evening so that he could work on it first thing tomorrow if he could, and let my office know that I'd be working from home tomorrow. I do hope that it's relatively minor and that replacing the oil pressure sensor isn't a terribly expensive job.