I have a 98 cobra and I recently got an alignment and they told me the the cross caster and toe are off. So i would need to replace? Every thing is stock. They were not 100% sure on this either. So do these things wear out. Ive only read if you lowered it or something.
Aftermarket camber/caster plates are not necessary if everything else is stock (suspension wise); but they can allow you to tune in a specific camber/caster setting if you are looking to tweak your suspension for autocross/roadracing/etc.
They are helpful to have when you lower the car too; what did the alignment shop suggest? Do you have a copy of the settings or a print out of the specs on your camber/caster/toe? If your current shop does not know, it might be a good idea to get a second opinion at a different alignment shop in your area that deals with mustangs...
On the paper says the cross caster is -.8, which says could cause a pull to the left which it does but not to much. They also said the passenger side lower control arm is bent. But then they gave me a print out of the camber/caster strut mount and said that should do it.
I have many Mustangs in my JY....some are hit really hard, and the control arms rarely bend. But it is possible. I fixed a 97 Cobra...wouldn't align, so I put a LCA on it.....and it took an alignment. They looked the exact same...you couldn't see any differences in where the one was bent...but it must have been. It brought my wheel forward. The strut plates don't really go bad...there isn't really anything to go bad on them.
If they are sure the lower control arm is bent, then that is the place to start. Replace the bent arm and then if the cross caster is still out, you could try the camber/caster plate. Caster is not adjustable with original equipment parts and should not need adjustment if suspension is stock and not bent or worn. Any known damaged suspension part should always be replaced for safety sake. The stress that bent it probably weakened it and could cause complete failure without warning.