Best course of action? I would say you should probably fix or upgrade your current gearbox. If you are willing to open it up and explain what appears to be the problem I'm sure we can walk you through it. As for $130, you can easily build a top end gearbox from the ground up for that, the king arms one is mediocre.
Personally I would purchase a gearbox shell (if needed) of this forum, I can link one if you need. Then salvage the working parts from your gearbox and purchase the rest. That should give you a good reliable gearbox with a tad of work. Up to you, if you decide to build one I can give you a recommended parts list.
Personally I would purchase a gearbox shell (if needed) of this forum, I can link one if you need. Then salvage the working parts from your gearbox and purchase the rest. That should give you a good reliable gearbox with a tad of work. Up to you, if you decide to build one I can give you a recommended parts list.