Here's my problem with using voodoo to get the valve to open.
It's stuck now. It will stick again. Only next time it will be in a live, running system, and pushing it risks weakening joints and putting stress on the bulkhead, risking far more problems than just a stuck valve. Those valves are known for this, and no one who has built a system once with them uses them the second time.
The plumbing on that tank was done in a hurry with no attention to detail, using the cheapest quickly available parts the seller could find. Judging by the number of couplers in there instead of clean pipe, the whole thing has already been sliced up twice to fix mistakes.
Tear out that whole line, and redo it properly, using new pipe, a new bulkhead unions and a gate valve.