Mine rotted out the valves in So Cal... so it depends on the vehicle at this point.
Depends on the year, 89?-2 fixed the head issues (they just crack in the normal places now
) and if an OEM one goes in 2016 its probably just age at this point.
Iffy parts support, it's not an off the shelf motor anymore.
None of them are as bad as a 2.8 nor as good as a 4.0
The computer requires systems knowledge to troubleshoot (miss-fire equals lean not rich kinda things)
Cam bearings (if PO was lazy)
Honestly, though deferred maintenance can force a rebuild on anything, on a 2.9 you can even defer the rebuilds in most cases. Mine had past Cali smog with a bad valve and 0 compression... and drove like that for 2 years...
The biggest problem for most people, is that it's not shiny enough; that is the eternal automotive fault.