Originally Posted by John E

I am reading two separate problems. First, the freewheel pawls evidently were not engaging, and flushing and relubricating the freewheel mechanism helped. Second, someone probably overused the smallest cog, wearing it out prematurely. This is a very common problem among people too lazy or ignorant to use their gears properly -- they just throw both levers all the way forward and ride in small-small crosschain, the combination which leads to the fastest wear of the affected portions of the drivetrain.