You should NOT weld. braze or otherwise join, or "fix" an hydraulic lines, they, ideally, must be run as a single length again, any Join will simply fracture... Also if they are developing "Pin Holes" this is probably due to the material breaking down, and like a "Cancer" it will simply spread, and fail at a probable inappropriate time, not as though there are any good times? As an aside there are "Joiner" kit available for hydraulic lines, perhaps, cutting and rejoining like this may be acceptable? but still i wouldn't risk it, run new ones.

Clean the place to be repaired with sand paper use mechanics wire which has been cleaned wrap the area where the leak is about an inch each side of it braze it completely all around will last for a long time has worked great for cracks that run with the flow.