Been there, done that, did this same job last week.
Brute force will eventually work at some torque level, but there is a more elegant solution...
You will notice that the balljoint stem is essentially 'clamped' in place. There is a split on the backside that the bolt squeezes closed to clamp down on the joint.
If you pry this split open, it will release the clamping pressure from the stem. Exerting some downward force on the arm while prying or wedging the split open may be helpful.
Do not open the split up too much, or you will have problems aligning the bolt upon reassembly (been there too). There is a notch in the balljoint stem that the bolt keys into, and you will want minimal play when reassembling so that everything is certain to lineup right.
I strongly suggest replacing the balljoints if they were not already on your list. Both the struts and the balljoints seem to have about the same lifespan. Why put struts that will last 100K miles on balljoints that only have 40K of life left on them (and vice versa)? I am biased here by the fact that one of my balljoints actually popped out of its socket while I was driving. Thankfully I was going very slowly over some speedbumps at the time. The 124 suspension design puts more stress on the balljoints than a MacPherson strut design would. The full downward force of the spring is placed on the balljoint whenever the suspension is fully extended, like when I went over those speedbumps...(or coming out of a high-speed depression, cresting a hill, etc.)
You may also want to think about those control arm bushings at the same time. Mine were toast. For the labor involved, replacing all of the wearing parts at once is cheap insurance against having to dissassemble the suspension again anytime soon. Plus, how great is it to have a like-new suspension with no play!
Pickle-fork separators usually damage the dust boot seal on the tie-rod end. I would be concerned about their lifespan from here on out. These things are certainly easy to replace at some later time if they fail, though you may need to pay for a second trip the the alignment shop at that time... My tie-rod ends were almost new, so I left the joint attached, and unbolted the 'steering arm' (or whatever you call it) at the steering knuckle assembly instead. This MB is the first car I have worked on that allows seperation in this way, so you may want to try that on the other side...
Good luck, and happy wrenching...