Can you replace a spring on an SRAM (SX4/X4) derailleur?

My chain has gone slack and my SRAM X4 derailleur seems to be the culprit, with cage now not returning fully to position when twisted (there is slackness in the movement). I've heard it's likely to be the spring inside the derailleur that's gone but I can't find anyway of getting the spring out (there are no screws or entry points I can see *anywhere*). Is it game over for the derailleur or am I missing something? All help appreciated!

Also I know the pics of the SX4 but I've been practicing on this before I opened up the 'real' one which similarly has no screws to get into the spring chamber!