Would not worry about it mate an less it starts making a bad rattling noise it’s not a part changed on mileage . I have seen the xt660 with over 30.000 on them still on same cam chain. Seen a cbr 929 with 97,000 miles on it still on same cam chain. If bike has been looked after and serviced regularly I would not worry about it. I have two 2007 xt660r both still on the original cam chains.