Oh wise ones! I need help identifying a component failure...

I have a 1974 Series III that partially rolled on me this past December. A lot of other things going on between now and then, so I'm only just getting a chance to tackle the underlying issue and I need some guidance about what to focus on replacing.

As background, I had parked my SWB at the top of a hill to open a locked gate and then cut several errant branches that were encroaching on the dirt road leading down the hill. I left the vehicle running but had set the parking brake; it was parked on a very slight decline and there was no indication of movement when I got out of the vehicle. I was only out of the vehicle approximately 3 minutes...long enough to open the gate and descend approximately 60 feet to cut several stray branches...I heard a noise as I was throwing the last branch off-trail and saw the vehicle rolling at me doing around 15-20 mph. I managed to get out of the way, but the truck ran about another 100 feet farther down the trail before catching a rut, bouncing off its right side (it actually bounced back upright), and then hitting an earthen embankment on the opposite side of the trail that finally stopped it. To its credit, the engine never stopped running, and was driveable although it had significant body damage to the right side body panels and front bumper. A "sh*t you" moment, if you will, when you briefly think about trying to jump in the truck and then realize the idiocy of the notion.

Clearly, the hand brake did not hold the vehicle. I have kept it parked in gear and with wheel chocks since the accident, but I need to make sure this doesn't happen again. To that end, what components in the transmission brake would be the likely culprits?

I'd like to do a focused parts replacement versus a blind wholesale replacement of components if possible.


And am I off my rocker to believe that a transmission brake, in good order, should be able to hold one of these vehicles stationary even on a slope?

Any input is appreciated.

Cheers.

Corey