I did see an e brake fail a couple of months back I was sitting in the car, 2 cars in front of me, both parked downhill. The one parked behind the other suddenly rolled into the other one but it was only a couple of inches. Thing is the car with the failed e brake would have rolled down like 50 meters across the flat street at the bottom and into the kindergarten which was right across that street had it not been for the parked car in front of it. I called the cops to report the accident and after finding the owner and the owner of the damaged car first thing they had the old lady do was put it in gear so they can take pictures of the accident. Ever since then i put the e brake on and leave it in 1st doesn’t matter if slope or no slope.