LoL, the title of your thread gives the incorrect impression that you purchased the machine from us!
Sounds like you've had some interesting problems. A Volvo that keeps an operator at the edge of his nerves for fear of sudden rapid deceleration (operator testing law of inertia), and the Hyster that wants to run but just can't.
I like your idea of installing an electric pump at tank and finding the air leak, pretty clever. You said you brazed the line, it now doesn't leak, but you would like to replace it because you don't like "patching things". Hmmm, sounds to me like you've "repaired" the line, not patched it. If you did a good braze job, it doesn't leak, sounds good to me. Call it repaired, pat yourself on the back, and let it roll.