Fixing inaccurate wall clock

This cheap wall clock cost me ~$3. After few weeks it showed up that it is quite inaccurate being late ~40 seconds per week. While these plastic cogs tend to wear after few years causing clock to even stuck completely in some position it was unlikely that this kind of defect was present from the start.

Crystal resonator used in this clock had no markings and I think it may be production recoil. After changing it to another similar size crystal decent accuracy of the clock was restored.
Further testing showed that with new crystal clock is slightly speeding, so 20pF trimmer was added for adjustment.