My 91 E300 4Matic is leaking alot of hydraulic fluid. I drain and change the fluid every 10,000 miles due to a small internal leak. i added 1 quart of MB hydraulic fluid back in december. At the end of February the reservoir was almost empty, I filled it with regular hydraulic fluid. One month later, i filled again, only now the fluid gushes out at highway speeds. I cant see any leaking hoses and the fluid seems to be coming out of the top of the case. has the internal seal totaly failed and the fluid is coming out of the vent or is there a hose on top of the case that I cant see?(or is the transfer case toast?)