Alignment Needed After Rear Ball Joint Replacement?
 

I have a 2000 Boxster S in to a new (to me) mechanic for a thunking/squeaking sound in right rear. He's diagnosed it as a bad ball joint which he has ordered. I gather this comes with the control arm.

Today he mentioned I needed to get it aligned after he installs the new part. Tires have always worn evenly, car has always ridden smooth. Do I really need an alignment after a rear ball joint replacement? Or is it something I should road test and see how it feels?

You should have the alignment done after and chassis part replacement.

If you are replacing the rear track arm (looks like a tuning fork on one end), neither end of that arm is used to configure the rear alignment (camber on the inboard end of the lower control arm, and toe on the inboard end of the toe arm, both of those control arms have a rubber bushing on one end and a threaded pin on a ball joint on the other end)

Even if the ball end was totally shot on the rear track arm, (which controls the caster, non-adjustable), in my opinion :) it would have a minimal impact on the camber and toe of that rear wheel.

I replaced both of my rear track arms and did not get an alignment, and was ok.

Compromise: take it to a place that offers free alignment checks :) Wouldn't hurt to get it checked...

In the rear, If you replace the lower control arm ('coffin arm') or the rear control arm, you should get an alignment. Forward OEM type track arm (non adjustable) or drop link replacement do not require an alignment.

In the front, Lower control arm, inner or outer tie rod replacement equals alignment. Forward control arm (from lower control arm to chassis) and drop link replacement equals no alignment.

I agree with that 100000%, alignments are cheap, $50 ish anyway so why wouldn't you.