Assuming you mean the tie rod end "boot", sure polyurethane will work and last longer. Indeed, I routinely install them on new tie rod ends and ball joints, instead of the thin rubber ones that come with them (not just Euro brand). If the ball is still tight and you see no rust, I would just wipe out most of the old grease, re-grease, and reboot. I think the primary purpose of the grease is to keep out moisture, but it also lubricates.

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1984 & 1985 CA 300D's
1964 & 65 Mopar's - Valiant, Dart, Newport
1996 & 2002 Chrysler minivans