well my dad has one in his truck, it's l/s capabilities were gone by the time he had 25k miles on it. he took it to the dealer and they agreed, so they rebuilt it under warrenty. i'm not sure how many miles he has on it now, but recently he has been complaining of the same issues. it's no longer under warranty but i dont even think it's got 50k miles on it anymore. it's still drivable, but doesnt work any better than an open diff. the other truck is one of my brother's friends, i don't have the full story but it's failure was bad enough that it wasnt drivable. he took it to a shop and had it rebuilt. had i known, i could have saved him a ton of money, but it's a little late for that. i dont know if the failure of that axle was a diff failure or a r&p failure or what. didn't ford recall a hand full of torsen axles because of something? maybe that explains at least one of those failures? all i know is that when i decide to swap in an 8.8 into my truck, it will be an explorer axle, not an fx4 axle.
on a side note, is there any chance there is a lunchbox locker available for a torsen diff? anything that doesnt require gear setup? how difficult are they to rebuild the l/s unit?