If you aren't seeing any physical play, they should be fine. I'd physically inspect them though.
Nylon bushings (both Delrin and Nylotron are in the same family) aren't very tolerant of misalignment - they will actually bust if tweaked - but are great for apps where there aren't any offset loads - like swaybars in a suspension system that truly locates the uprights with control arms.
Urethane under load tends to "creep" and deform, if squeezed one way and left there, but will be better if there is some misalignment or offset motion, like if control arm pivots aren't exactly on the same axis.
K