Possible Cause of Spider Gear Destruction

repetitive shock loading... doesn't have to be a one big burnout thing....
heavy load or a hill, uncapped/ cobbled or ridged road due to heavy truck or bulldozer traffic... constant variation in traction due to wheel hop and shimmy breaks those tiny gears and fatigues the axle shafts.

gears 2.94:1 are hard to turn, tall gears, so slamming a bunch of torque at the rear end every time to get going fully loaded.....not high tailing it outta there, just constantly pushing it.... is gonna involve shock loading. especially if the cone washers were worn giving bigger than normal side gear clearance.

whoever drove it, drove like it was the "company's" truck not their own.... not paying the repair bill, gotta get there in order to get back for my lunch break...etc

this is why they used a modified centre with 4 pinion/spider gears on 2.77:1/360 v8 equipped cars, or at least they did in Australia, a land with a huge amount of uncapped trails and roads, once you get away from the suburbs, you can if you wish, drive for 100s of miles vibrating your teeth loose, fantastic cure for constipation.

sure grip clutch based, or cone diff would work well. the Aussies made do with a 7 3/4 behind a 318/904.. they lasted ok in Utes and vans... 1/2 an inch more gotta be worth something