Easy way to check the rear accumulators is to put a foot or knee on the rear bumper and bounce the car. If only the tires bulge, no wheel movement they are DEAD. If very stiff (stiffer than the front), they are going.
Not too bad to replace once you get the panel out, it's usually stuck on the front edge. You will need to get the rear jacked up off the wheels as the rear end will drop considerably when you remove the lines otherwise.
Get a quart of hydraulic suspension fluid, too, you will lose almost that much. Be prepared for it to drip out of everything. Line connections for accumulator are under the car, accumlators inside (why?????).
The struts almost never leak unless driven for quite a while on bad accumulators -- the overpressure blows the seals out. They are a bit dear....
1972 220D ?? miles
1988 300E 200,012
1987 300D Turbo killed 9/25/07, 275,000 miles
1985 Volvo 740 GLE Turobodiesel 218,000
1972 280 SE 4.5 165, 000 - It runs!