Back in the late 60's I worked for a Shell station and the old time owner had us lube the parking brake cables as part of a normal lube job. The neighborhood had a lot of steep hills and everybody used their parking brakes or suffered the consequences! Some years later my father-in-law borrowed my dad's '86 Mitsubishi pickup (2.0 & 5 speed) and parked it (in 2nd gear, no P brake applied)on a slight grade in his driveway. During the night the truck started moving backwards as compression bled down, hit several trees on the way down and destroyed the bed! The bill was over $1,200.00 and a bone of contention for years. FIL wanted my dad's insurance to cover it and dad wouldn't have it. Use the P-brake and avoid problems, that is what it is there for.