I would just like to add that those systema drop in gear boxes usually require to be opened to me reshimmed sometimes. Depending on how long they have been sitting on a shelf they may require to regreased as well.
Lets take a quick second to review your options:
1) Open your current to prefer repairs and preventative maintenance.
At a ball park cost of around 50ish dollars depending on the severity of whats wrong currently.
2) Buy the Systema drop in box you wish and drop the 200 dollars on an highly unneccesary upgrade that may require just as much as option one.
3)Instead of buying the systema drop in you could buy a JG drop in. However, just like the systema drop in you may require to open it to reshim and either regrease or degrease the mechbox. Estimated ballpark cost of this option would be around 100 dollars.
"Its only a little bit on fire"