You don't need a spring compressor to do this job.
Just a support underneath the axle area.

I have had a couple of W124's where the strut has come off involuntarily. The spring does not fly out. It's too long. Still you must be careful.

Unless your struts are heavy duty sports stuff you will be able to compress them enough by hand to remove the top strut mounts.

You will do the first one in about 45 minutes - the second 15.

You cant tell whether or not the struts are faulty without taking them off. - unless they are leaking. The bounce test is inconclusive on a W124.

You may need a wheel alignment if you remove the strut altogether.

The original struts will have a dab of paint swabbed across the central area. All original parts are daubed with a swathe of paint - that's how you tell if original or not. Even some bolt heads have the paint swipe.