If you have the time order one of these
https://www.ebay.co.uk/i/15387875729...hoCy1sQAvD_BwE
It is worth every penny and is truly amazing what will move once it has had 10 mins to do its thing.
I have used it on exhaust bolts that looked like they would never move. You need to shake it before you spray and once you hear the balls rattle give it a squirt.