wadey

If you have a leaking rear main seal should it leak while the car
idles in the driveway or only under load on the highway? I thought
i had a bad seal but i don't get any oil while the car idles.
thanx wade

Smokehouse69

I've noticed the same thing with rear main seal leaks (and other leaks) in the past. My leaks have always seemed to occur when the car was parked and allowed to cool for several hours. So I assume that the heat produced by the engine cause enough expansion that the seals stop leaking.
As far as your under load observation I guess that oil pressure might have soemthing to do with it. At idle my car is running about 30lbs of pressure, while cruising at 2500-2700 rpms I am running 55 psig of pressure.
A bad PCV valve or a plugged breather can also promote oil leaks on a running car, vapor pressure inside the engine can build up and cause things to leak.

Racer16k

It might leak more when the oil is sloshing around in the pan. Either way it's not too hard to fix in a vette. Messy, but not hard. I just changed one in my 1954 International R100. It had the rope type seal. No way I was going to be able to get a new top half in there, so replaced the bottom half and called it good enough. This truck would leave a spot overnight the size of a mouse pad (bad leak). Now I rarely see anything at all, and even then it's like pencil eraser size. On a truck this old that is pretty good.

Frankenvette

I have a leak at the rear of my intake manifold. The oil drips all the way down to the backside of the oilpan making it look like a rear main seal leak. I have already changed my rear main seal and thought it was still leaking when I discovered the oil leak at the intake.

Vetterodder

Jim makes a good point. A lot of rear main seals have been replaced due to leaks that actually originated elsewhere. I've seen front seal leaks, timing cover leaks, oil pan leaks, intake manifold leaks, and valve cover leaks that ran along the block and wound up dripping from the rear of the oil pan. If the engine is kept clean it's a lot easier to identify the source. If the engine isn't clean, it's almost impossible to tell where the leak originates.

Paul L

The rear seal is above the oil level in the pan. I cannot see it leaking when not under pressure.