Dark brown fluid? Uh oh.....should be clear......
Is is over filled? This fluid is continuously cycled during operation, and will tend to heat and expand. The reservoir should be filled to the mark on the stick, no higher. Mine is about 3" from the top, I think.
Check the previous postings on the hydraulic suspension. The other thing this may be indicative of the hydraulic pump seals going, and engine oil leaking into the system. Although, it usually goes the other way...(hydraulic fluid into your oil)...as the hydraulic system pressure is much higher than the oil pressure. I believe you can remove and reseal the pump located on the front of the engine, if this is the problem. Search on Fastlane for a kit? I do not know what the proper name for the kit will be, if it exists.
1989 560SEL (172k)
1989 325IC (122K)
2004 Suzuki Volusia LE (3500 miles)
2005 Yamaha Road Star (20 K miles)