Mines the same after 5500 km´s. (Sort of glad I´m not alone... ). I´ve arrangedfor it to do it´s normal oil change and for them to sort it out and what they told me is that´s probably a defective seal of some sort (bikes got only 6 months ). I´ll let you know what happens.
Mine 2017 XSR700 is having the same issue. It's reaching its 7000km now, but the problem appeared at about its 3000-4000km, similar with yours.
I've sent it to the dear twice, the first time they changed the Gasket and O-rings, but didn't solve the problem. The second time they changed the side case of the gearbox the week before last week, but I found it's still leaking, this morning!
Where could the problem be? This makes me really upset. Have you sorted it out?