If your side brush is slow sluggish not spinning - check this on Neato D7 BotVac and other models - YouTube
Neato Botvac D7 review: Offers powerful suction but lacks some features given the price | Android Central
3Pcs NEW robot cleaner parts Vacuum Series Red Rubber Belt for Neato BotVac series belt by the Side brush|cleaner parts|vacuum cleaner beltrobot vacuum cleaner parts - AliExpress
Side Brush Motor For Neato Botvac D7 Vacuum Cleaner RF-500TB-11660 - iNeedParts