AGM Scar L upgrade help

[Jambo17]

Hello, I recently got into airsoft after briefly playing 5 years ago, at the time I bought an AGM Scar L and it's lived in my mates garage since apart from the odd shooting of targets in the garden. I dusted it off and took it for a day at my local site and it performed ok-ish. I naturally assumed it'd be below par given it's had zero maintenance for 5 years. So I asked around and a few recommended upgrades where a madbull v2 tight bore, a lonex titan a2, a new m120 spring, bucking, shimming and a general maintenance. Well feeling a little over confident from watching youtube vid's I've dissembled the gun upto getting into the gear box. I just cannot for the life of me remove it from the polymer housing! I've removed all instructed pins, disconnected the fire selectors on each side, in all the videos at this point the gear box just pops out but mine is stuck, how on earth do I remove it?

 

The second question is have is regarding the hop up / gearbox replacement - basically having phoned a couple of websites for advice I was basically told to bin the gun and get a new one.... If I could afford to then I would but it didn't answer my question, I've seen the madbull ultimate hop up and wanted to know if it'd fit (or any that would) and what pre-built gearboxes would fit the scar. Down the line I'll be getting a new decent gun but that's a ways off and I want to make the most of the one I have with bits I can get over time, hence the upgrades. So any help would be most grateful.

 

Cheers