A few thoughts on my 40 yrs of continuous ownership of #4366:
I've fixed a number of Panteras with 'bad wheel bearings'. In most cases, the bearings were perfect but the OEM stub axle was worn. And by 'wear', I mean maybe 0.001" of metal missing or pounded into a tiny ridge around where the bearing race runs. To check these dimensions, one needs a five-place 1 to 1-1/2" micrometer or you're just guessing. What happened at the factory that originally made the axles was, some of the hollow stock axles were machined slightly undersized for a proper press fit into the wheel bearings. OEM bearings by SKF or anyone else requires a 0.0003"-0.0008" interference fit. And yes- all those zeros are important. A 6 inch calipers or Harbor Freight mic' won't tell you this.
* Many of the OEM axles were made with NO press-fit interference as mentioned. Compounding this problem, bearing-race steel is super-hard while stock stub axles were made of mild steel. This combination only works IF the press-fit dimension is correct. If the fit is loose for any reason, guess which one suffers? Right- the softest one.
* Nowadays, repro axles are made of 300-M steel and are solid, not hollow: better steel and a 20% stronger design. I no longer weld-repair stock axles- the repo's are simply better all around. Don't waste your money on hollow OEM axles with any sort of repair.And the nuts are supposed to be one-use-only.
* Big sticky tires: If stock axles don't wear from inadequate press-fit, they break under even stock engine torque with oversized modern tires and sticky rubber compounds. Real racers know that perfect, properly assembled stock rear axles and race tires were mostly good for about 4 hrs of intensive racing before the axle broke at the shaft-to-wheel flange. A dozen laps of club-level open-track is not 'intensive racing'.
* To check the ball-bearing-vs-tapered-rollers thing, over 20 years ago I converted ONE side of our Pantera to tapered rollers (my own design) and the other with stock ball bearings- with correct press fit. They've both been on our car for coming up on 50,000 miles- none of them very easy. No problems from either side so far, so no advantage either way. Theoretically, ball bearings should run cooler but I've seen no measurable difference on the street.
* Tightness of the axle spanner nut: the SAE says that a fine-thread steel shaft & nut of 1-1/2" OD will shear at around 1100 ft-lbs. At only 400-ft-lbs of torque as used on most Panteras, the inner bearing spacer, again of mild steel, will indent against the much harder bearing races and get shorter over time, running 400-500 bhp through the assembly. Some shops and owners face the spacer smooth so it looks nice. Re-tightening the nut with a now slightly shorter spacer forces the nut to thread down the axle a little further. At some point, the axle runs out of threads so the nut is really tight but the sandwiched assembly is a bit loose. Bingo- another 'bad wheel bearing'.