Ayuh,.... When ya have the drive off, for it's Annual service,...
Run yer fingers all over 'em, 'n check for cracks in the creases....
Ditto the shift cable bellows...
Figure 5 to 8 years of life, dependin' on conditions encountered...
With the cost of replacement ujoints, gimbal bearings, seals for the drive upper, yokes to replace old rusty ones, every 5 years would be a good idea. It's a lot cheaper than the repairs.
A friend of my dad will actually load the bellows up with silicon if he finds a rip lol! Don't do that.. I found a rip in the shift cable bellow u could fit a dime through, so new bellows are going on.
For a mechanically inclined person, how difficult of a job is this really to do? I've watched the YouTube videos, seems straight forward, but, you never know...