Gg Gec36c Hop Issues

[Brotherhood98]

I purchased a new g&g GEC36C last year and after a few games it has lost the ability to apply any sort of hop to bb's so I'm guessing it needs a new rubber?  Whilst the gun is apart, is there any modifications that you think may be worth doing?

Also, has anyone got a guide/instructions for dissassembly?

Thanks 

Jake