Hi
Murray,I agree mate, heat is your friend, but there are some situations and areas on machines where you can't use heat, in that case Penetrene is a safe way round it.

Well obviously every situation is different and common sense has to prevail.
If you are not confident or capable of using heat for the appropriate situation, then you may need to find some one to do it for you or find another method.
In this situation, I would have used heat. That nut looks like it may not be threaded all the way through.
If that is the case, no amount of soaking would have penetrated that considering it would have be wound up tight to the frame.
This is just my opinion.