[svxistentialist]

Break free fluid is good advice. A good class of penetrating oil left to soak on the bolt overnight will usually shift it.

If that does not work, a good folk remedy is use some brake fluid on it. That stuff really soaks in, do not put on tons of it on and no way let any of it touch paintwork or rubber belts. It will loosen your bolt.

Use a large half-inch drive socket to loosen it, should have strength enough to loosen without a bar. But use a bar over it if need be.

Joe