Mp5 break down help

[spyther]

Hello, my friend recently bought an MP5 RAS which has had bad problems almost from the beginning. It'll fire a few rounds, and then lock up. We are curious to take a peek inside it (and yes we know we shouldn't take apart the gearbox unless properly instructed, etc.) but we have a question about how to take the gun apart. We can dismantle most of it, but we run into a problem trying to get the lower receiver off from the upper receiver. We want to get into the gearbox and motor area, but we can't get the main body pieces seperated from eachother - even though we unscrewed just about everything we can find. We think maybe the selecter switch inside the gun might have something to do with it, but we don't know how to completely remove it without taking apart the receivers, so can someone perhaps help us out on how to remove said parts. Or perhaps a comprehensive website with such info, the instructions that came with the gun are a little confusing at best, so we are looking for something a little bit more explanatory.

Thanks a lot guys

[spyther]

Okay, I was missing the 2 screws behind the motor. But I have another question. How much does a fully assembled gearbox go for? And if I were looking on a site so buy them, what would I look up? When I look up gearbox, it just gives me the box itself.

[attack-beaver]

most complete gear boxs can start at 119USD and run up to 220USD so pick wisely and make sure the FPS is low enough u can use the gun at fields.

[Greylocks]

Look for the word; mechbox. Or full upgrade kits.