Discovery 2 2004 TD5 clutch / brake fluid.

Discovery 2 2004 TD5 clutch / brake fluid.
What is the correct type of brake / clutch fluid for this vehicle? Owned from new and nowt been done to the hydraulics except a clutch slave cylinder 3 months ago. Reason for the question - entrusted a garage to fit a new slave cylinder but he convinced my wife the gearbox was failing as it wouldn't go into gear properly. I insisted he changed the slave cylinder first and it was better.... but not much. I bled the cylinder two weeks later and the fluid ejected was dark grey to black. Pumped it through to clear fluid (added DOT 4 new bottle) and the clutch was damn near perfect. Yay!!
Noticed a leak from the bottom of the bellhousing onto the crossmember last weekend; no time to investigate further until this weekend - although the drips on the path washed away in the rain which suggests water soluble rather than engine oil.
I think all the sh*t from the old cylinder was not flushed out before fitting the new one. I think they just unbolted the old and fitted the new then bled it... sort of.... and the sh*t has killed the new part.
Any views on this and which brake fluid type were these fitted with from new - hopefully DOT 4 and I haven't ruined it?

Thanks in advance,

Steve.

dot 4, the black is usually seals deteriorating

Thanks James!
I was surprised that a new cylinder should contain such dirty fluid; don't really trust the garage to warrant the job - they'll just condemn something else to cover it. So I've got a new cylinder due today and a vac bleeder as well. What a great way to spend a sunny weekend....... I need to get out more......

Steve.