Reply to "ZF Horsepower Rating"

Box-stock ZFs? Well, I'd guess that most are, since new spare parts (except for the 3 oil seals and side bearings) are almost non-existent and very complicated to install. There are no adjustments except thru selective parts selection and (scarce) steel shims. The only real variation might be switching ratios in the ring/pinion or possibly the 5th gear-pair for mileage or speed improvements, and those require total disassembly with specialized tools.
100% of new stock parts since the late '80s have come from Lloyd Butfoy of RBT whose father bought the name, manufacturing rights & all spares for the 5DS-25/2 transaxle from ZF. So either you buy salvaged parts or non-stock pieces from a number of vendors, or new parts, and all new parts will have come from RBT.
Incidently, even the gaskets are critical since their thickness controls backlash and preload, as well as whether they retain lube inside. I don't advise skimping on ANYTHING in this precision $7000 assembly! Lloyd is sometimes difficult to reach but is extremely knowlegable in all aspect of this transaxle; it's all he does since he was a kid. He's willing to talk but is extremely busy, so free advice and brain-picking is hard for us to do.