['63GENIII]

I think the 221s have a reputation for being a durable enough unit since their inception. I ran the one I have behind a 396, towing or hauling anything that I wanted for many years without much more than noise or the heat that is common to them.

They are a little quirky though in that they have an idler gear that power is transmitted though whether you're in 2wd or 4wd. The result is lower driveline angle but also extra heat due to the extra gear and bearings. This also makes it critical to keep it full of clean oil. Good bearings will help the seals do their job and keep the oil where its supposed to stay.

As short 3/4 said, quality bearings are still available as are the seals. Some of the other "hard parts" can be source online used. If you're just driving it occasionally, Id do a gear oil change on it and keep an eye on the level until you know it doesn't leak. If it's a leaker, they're clothes pin simple to rebuild.

As far as why the one in the first post broke... could be a million different things but I don't think that would be a good example of a 221 common failure. The oil in that thing looked like roofing tar. Probably original transfer case oil in it.