Help!

Hi, i have been loosing oil on my triumph street triple 675 2016 and i have been seeing oil drips from oil filler cap while riding hard, last 3-4 days i have ridden 300-400km pretty hard 1st and 2nd gear and lost 500-600mg of oil could just the o ring be the problem? i have changed it with knew one and one that was on it was flatten and hard i couldn’t feel rubber at all while pushing it with my fingers