Clutch Slip, Compression Loss, or Just Too Steep?

[tre_oh]

I rolled the Box' up a slightly inclined driveway in 2nd gear and killed the engine. Living on flat LI I didn't bother to tug on the e-brake figuring the car was fine. I went inside and came back out about 15 mins later to find the car sitting at the bottom of the driveway! Whoa, the doors were still locked and the tranny was still in second gear. Luckily the car had only rolled about 6 feet and came to a stop once the rear wheels left the incline; no damage, just a new found belief in e-brakes. I poked around on the web to understand this and the "Car Guys" said this could indicate a loss of compression in the engine. They recommend putting the car in first or reverse AND engaging the e-brake. Anyone have a similar experience or deeper insight?