The E34 M5 came with a self leveling rear suspension. It's common for the rear shocks to leak when the accumulators are blown. The accumulators are small "bomb" shaped nitrogen filled bladder canisters that live above the rear axle on each side of the car. When they have failed there is no cushion for the hydraulic fluid and is forced through the seals of the rear shocks. Left alone the seals will become completley shot in the shocks and additional costs will be incurred. Like $500 a side, USD....the accumulators are only $100 each and replacing them is really no guarantee, but it has been known to work on several cars I know, and really improved the ride to boot!
If your car is just leaving a little piddle spot, then chances are they will work, if it's pouring out, that's another story....if you do decide to replace them, you will probably need the short hydraulic lines also, as they are usually ruined removing them.
Your other option is more drastic and involves the elimination of the hydraulic rear suspension and replacement with conventional springs and shocks while looping the hydraulic lines so they will return to the pump and circulate only.
In either case, check the fluid level in the reservoir under the hood, you don't want to run the tandem pump dry...
Jr