Engine sounding a little rattly

[Mchancox]

Hi all. I have a FZS600 and have had it a few months. It is an 02 And has done 20,000. When I bought it the oil was clear (good sign) and all things sounded tight. It has had a few revs of late and worked a little hard. I've put 2000 on it and the engine is sounding a little slack. Sounds a bit rattly on the top end and engine oil is black and has the consistency of (doesn't contain) water.
Suggestions other than don't work it so hard please?

Cheers.