Don't know that a leaking primer bulb can be repaired. Most likely, you have to replace it. You don't want to forget the routing of the fuel lines!! You might want to make a drawing of the routing before you remove the primer bulb.
Most primer equipped carburetors use a diaphragm equipped with flapper valves in between the primer and carb. This allows fuel to be drawn through from the fuel source one way, then pushed through to...
Depends on the model. On the toro single stage powerlite CCR it's simple. On the back of the "bulb" (black rubber button) is a white plastic part. Slide it down and feed the clips through the cover....