The l&r rear axle seals- rear axles complete are $150.00 rebuilt then labor $700.is reasonable if the axles are rebuilt as needed, not just new rubber boots installed.
Power steering- check the gasket on the resovoir its a few dollars & anyone can install it. I did this and put in some stop leak in my sec and now it does not leak at all. It previously leaked about a half pint every week or two. I know some will scoff at stop leak(i did too).Savings-$600.00.
I would fix the flex disk first to make a long story short,then steering shock(a $50.00 Part). Then see if you could have the engine cleaned, change the oil often with 20-50.(worked on my (1991 300e 4-matic) try to isolate the leak or simply have the head retourqued along with the timing cover bolts. However, someone once told me retourqing the head could actually make it leak more, although this theory has yet to proven (to me anyway). It really depends how much you want to spend. Hope this helps.