@alanf
good question. my Shimano PF92 on my MTB went bad after 3 short months of mild XC rides and no jetwashing. replaced with another of the same because it was cheap and available
I’ve already replaced the Shimano PF86 on my road bike after 6 months, again with the same for same reasons.
the wheels manufacturing unit with angular contact bearings in aluminium alloy which screws together looks good, mainly for bottom bracket stability
I’m sure one of the big factors in short bearing life on these nylon PF units is the axle placing high loads on the bearings whilst pedalling, perhaps caused by slight misalignment. no idea what bearing type shimano use in there? might just be radial cartridge rather than angular contact.