do I need new shock absorbers?

I noticed one side of my rear was lower then the other today. I did some measurements and found my shock absorbers are not even. (see pics)

I read in my manual that I should only replace an absorber only if its broken or badly leaking. I dont see any leaking but I'm not sure if its broken. the manual also says I dont have to replace both at once.

So the questions: (opinions matter)
1) should I pull it off and test if its broken or just replace?
2) if I replace one should I just replace them both, maybe the front ones too?
3) what absorbers would you recommend?

4) oh and most importantly, how dangerous to my health and the health of my car is it to drive around with things as they are?

Its a 69 dart with a tow hitch on the back. I may wish to tow some things in the future. street car (daily driver)

TY