Hayes Mountainbike Brake Handle Leak Repair

[TayS]

I am in the process of disassembling a rather old set of Hanes Hydraulic Brakes (I don't know the model because the leak stripped the paint off), but I've gotten stuck disassembling the handle.
I'm pretty sure the leak is coming from or underneath the boot, but can't confirm it until I take it apart further. What's holding the handle in appears to be a press fit pin, but it has retainers of some hard plastic or metal holding it in.
Any ideas or suggestions for how I should go about addressing this problem? All input is appreciated.

 

[Big John]

Never tatted with one of these but looks like it could be a circlip. Stick a pointy thing in and prize it off?

 

[TayS]

Never tatted with one of these but looks like it could be a circlip. Stick a pointy thing in and prize it off?

Tried it, it seems to be a type of hard, but thin, plastic, and trying to pry it out via the little slot only deforms it.