Mechanics and Fixing Any Questions Answered

Ally fork?

Get a decent penetrating oil, Kroil is my go to, expensive in the UK but pays for itself in the first quarter of a can every time. Oil, tap, days, oil, tap, days. Don't even bother trying to move it the first few days. The more valuable the item, the longer you leave it.
Get geodore or knipex pump pliers the really good grabby ones, again, pricey but pay for themself within the first few uses tbh. Wiggle back and forth the smallest amount, often for an item that failed during loosening, you actually want to tighten it first, get the threads pushing the other way on the fastner. Can use heat, but wouldn't in that situation.

Welding a bolt on the end, MIG if your good, TIG would be better, more control and less heat. Want the absolute smallest amount of heat pumped into that tiny alloy fitting in the fork.