I am pretty sure my rear passenger strut needs.

Dandy pictures. Notice the oil on the spring and strut body? That's supposed to be inside the strut. This one has been leaking for a long time. That alone is cause to replace it, but left long enough, the shaft will become sloppy where it comes out of the top of the strut body. That will cause a dull thumping sound.

The yellow disc is called the "strut cushion". It stops the hard hammering action when the strut bottoms out over large bumps.

The struts are always replaced in pairs unless they are very new.

Knowledge is one thing I can share without losing any!

The hammering on the cushion caused it to fall apart and fall off. That can be aggravated by weak coil springs that let the car sit too low or bounce too low, ... Or if you have too many dead bodies in the trunk.

Normally a part of any alignment is to measure the ride height and correct it if necessary. That isn't as critical on smaller cars with strut front suspension but it was a real big deal on older, heavier cars. On those, the three main alignment angles could be adjusted on the alignment rack to produce good numbers, but you'd still have horrendous tire wear caused by the upper and lower control arms going through the wrong arcs as the suspension traveled up and down on the road. Those alignment changes are much less severe with strut suspension because there is no upper control arm to be in the wrong geometry.

An additional problem with your car is it's real light in back so weak springs are less likely to cause low ride height. First you have to measure it and if it is below specs, you know the springs are weak. If it's near the low end of the acceptable limits but still within specs, you have to consider the ride quality. If it bottoms out on bumps with only one girl in the back seat, it may need new springs. With two girls, (or one who's the equivalent of two), it can be expected to bottom out because the springs have to be somewhat soft to maintain the ride quality when the car is so light. It can be hard to judge what's normal, but if you feel the hard pounding over only larger bumps in the road, the cushions may be all you need.

I should mention too that those cushions are usually a dealer-only item but you might have to special order them in advance. Whether or not they stock them is determined by the past sales history and the age of the car.