DOT 3, 4 and 5.1 can be mixed, the only difference is their boiling point. DOT 3 should be fine for road use, I use DOT 4 as that's what I also use for the 900. Do NOT use DOT 5 as that is silicone based, unless that's what's currently in the system or everything is new and the seals are rated for use with DOT 5.
Thanks 'melle' I hadn't realised the difference was the boiling points. I thought that one of them 3 or 4 did old rubber seals in. Cheers for the quick response.