I bought a bike a few days ago and the rear shifter isnt working. At first it had zero resistance so i took it to the bike shop and they sprayed stuff in it but they said they couldnt really do anyhing because they didnt have (said something about a tank) but he told me that i should just spray WD-40 every so often and see if it fixes anything. So i been spraying WD-40 and now it shifts but if i click the shifter to hard it stops working again. If i wait about a min, its like it resets and i can start shifting again. I can shift down but its only when i try to shift up that i have problems. Anyways will this problem get fixed or am i going to have to look for new shifters?