Oil leak and oil change

Hi guys.

At first I wasn't worried as every couple of weeks I'd see a couple of drops in the floor, but now it's just getting absurd. The bike's leaking oil and the quantity has been steadily increasing - for some reason i can't quite understand. The pics above were taken yesterday - after I used the bike the day before, so you can see how much it's leaking, ATM.

My questions would be:
First, how can I check where the leak's coming from, exactly, and what can I do to stop it?

Second, I need to add more oil. Can I just buy any random oil and mix with the one that's already inside..? I have no idea what make it is, so won't that be a problem?

Thanks so much for your help..!

N.

Have you checked your oil sight tube? The fuggers always leak sooner or later and the pattern you have there looks consistent with a tube leak.
As for adding more oil, just stick in any reccomended grade of oil. Mixing doesn't matter. A full synth 10w 50 or 10w 40 - it'll be fine.