[-Spitfire-]

This is the most common issue I've run into with these TBH. This is the one time that soaking your bucking in silicone oil might actually help (try other solutions first obviously, as reason for failure can vary).

 

[-Spitfire-]

The hop up unit on these guns break easily.

Yup. Like I said, number one failure point that I've seen... However, or can be caused by the bucking drying out, which silicone oil can help reverse sometimes.