The factory BJ's use a plastic bearing that wears out over time, but doesn't grind so much from lack of lube. You're doing well to still have the originals and should just factor in replacing them eventually. They typically won't squeak so much dry due to the plastic, as much as just develop a gap that makes a clunk noise from the play in them, before complete failure. They don't always clunk, should be inspected for excessive play.
The lowers can have just the BJ replaced but the uppers require a new control arm that they're built into (some aftermarket replacement uppers do have replaceable BJ's but you need that type to do upper BJs alone the next time), and an alignment done afterwards.
A quality sealed, plastic bearing BJ can have a good service life, especially considering you already got 22 years out of those, but they are not as good for loads, or impacts like potholes, as an all metal greaseable BJ.
