Dirty clutch fluid

[ungeheuer]

Just change the fluid once a year and don't worry about the color. 

This.

A good quality DOT4 - I like to use Motul 660, I'm sure there's others equally good.

[MonsterHPD]

I think one it turns black the only way to reverse the situation is disassemble and clean everything.  Just change the fluid once a year and don't worry about the color. 

All my ducs (not that many, but anyway ....) have been like that. In the begining, I worried about it and changed the fluid, but with age-induced laziness setting in, fluid changes started happening only when made necessary by other causes. So far, I´ve never noticed a difference this way or that.

Infrequently, if not renewed as per above, I do pump thru some fluid and top up the reservoir, but that´s it.

May not be the correct way, but it has worked so far 

[d3vi@nt]

That rubber bellows was just there to keep out the grime. The seal is inboard of that. I think it's just heat that does it.

The open unit allows for a lot more ingress, particularly if/when the bellows fails. Which would accelerate wear on the inboard seals. The slightly later units did away with the bellows and instead sealed up against the case. At least in my case, the closed unit cleared up my issues with dark fluid. Although, at 20+ years, I suppose all seals and OE rubber lines could be suspect for contributing to suspended particles.

[greenmonster]

Not worried about colour, it`s that the the function gets worse.
Season almost over, will try other fluid next year.
What makes DOT 5.1 a better candidate?

[Howie]

Higher wet and dry boiling points.