Originally Posted by
Nessism
I'm wondering if I should remove the rear derailleur completely and soak it in mineral spirts to clean it?
Try shooting some WD-40 or solvent of your choice on the pivots with the wheel removed so you can manually push the derailleur checking for stickiness. A longshot but possibly some crud is stuck between the return spring coils which could cause derailleur to hesitate sometimes trying to move all the way to the small cog and some solvent might help remove as well. Also, how many miles do you have on this derailleur? Could be just wearing out too.