carburetor wear out

i have an issue with my xp 800r on trail for the way up and the way down the engine doesn't want to rev down by itself i have to hit the brake for drop the rpm and that problem it always between the parking lot(i'm not sure about altitude i was at boulder and frisbY) i think it's somtething like 400 meter ant 1500 meter after that they just run perfect i bring it to my dealer and they told me brp claim they have and issue with the carburator the plunger for air/gas wear out and they let some air to go in even if you release the throttle and make that one run lean and doesn't want to rev down only way to fix it change the whole carburetor for now it's not bad that one is warranty but next year i'm gonna have the same promblem (i make around 2500 km/year) somebody seen that before and find something for fix that????