According to Spielberger, the Panther was doomed to unreliability from the start. He says, "Since it was envisaged to produce the Panther in large numbers, production costs of various subassemblies would have to be kept to a minimum...If it had been possible to foresee what difficulties the final reduction gearing was to cause, it would have been a much better solution to have selected a more expensive final drive which provided a greater degree of reliability. In the end, the final drive proved too weak to handle braking with the Klaue disk break [sic] when steering through tight curves. The use of epicyclic gearing for the final drive hinged upon the bottleneck being encountered in the supply of gear cutting machines for producing the hollow gearing. When passing judgement on the double-spur final reduction gear it should be noted that the high-quality steel originally planned for the spur gears in the final drive was not available for mass production and was unexpectedly replaced by VMS 135 (today 37 MnSi5) tempered steel (not as suitable for this purpose)...
"The final drive (gear teeth and bearings) was the weakest part of the Panther. It was a risky proposition to use a spur gear system for transferring the drive power - especially considering that the available steel during the war did not have a particularly high stress tolerance. A better solution would have been to use an epicyclic gear system; a prototype final reduction drive using planetary gear reduction had already been tested and had performed flawlessly. However, as mentioned previously, a shortage of gear cutting machinery for the hollow gearing prevented this type of final drive from being mass produced. In order to bridge the gap a final reduction gear system was installed in front of the main gear drive, but due to installation restrictions its mountings were far too weak and could not be strengthened. Because of gear teeth breaking under too great a load and the weak mountings, the gears were pushed out of alignment - virtually guaranteeing mount and tooth breakage.
"The general consensus in the industry was that inner-toothed gear wheels could not be produced due to a lack of proper machinery. This meant that a final drive using planetary gear reduction and pre-selector spur gearing - found to be reliable in company testing - could not be installed in production tanks. All attempts to improve the final drive met with failure, despite the offers of a special bonus as an incentive..."
To quantify this a bit, Ristuccia and Tooze in "Machine tools and mass production in the armaments boom: Germany and the United States, 1929-44" note that Germany did make strides in increasing the number of gear-cutting machines in service, going from at least 10,407 in 1939 to 28,621 in January 1945. Even with these increases, compared to a US metalworking employee there were only 0.74 gear-cutting machines per German metalworking employee in 1945.