My tumble dryer doen't tumble without a shove?

My Hoover HVN380 will noy tumble. I have replace the belt as i thought it may be slipping. but no change. I have the top off and if I give it a quick shove on the top of the drum, it works fine until it stops to reverse, then it gets stuck again until i give it a shove. All is clean and bearing is greased. If it was a washing machine i would replace the brushes, all i can find is a whole motor replacement at £80. Butthe motor seems fine, what else could it be???