1986 Astro Van 4.3 L Developed A Major Oil Leak

this is the carburetor automatic rwd 4.3l engine that was working great for it's age. It burned a little oil, but had no leaks. The other day I was checking the levels and saw the oil was a little low, so I filled it up. I now realize the van was on a hill and the front was higher than the rear, so I may have over filled it. A couple days later the oil can indicator came on and off on my way to work (about 60 miles since I filled it). I got to work and saw the oil was no longer on the dip stick and there was a line of oil on the street. I looked under the van and it was covered with oil and grime but no leaks was noticed, I'm guessing it only leaks when the engine is running. Is this a good chance the oil pressure sender has sprung a leak? If not, what do you suspect?