Agitator barely moving and the bolt is not stripped

Hi I have an older Whirlpool Top Loader Washer Model LA5100XTW0 and the agitator barely moves when washing clothes. I removed the cap of the agitator and the bolt was completely out. I tried to tighten the bolt back in but it would not tighten. I was told that the gasket centerpost was the stripped part. Is the gasket centerpost worth replacing on this older model? How hard is it to replace? I was given two other solutions: 1. to rethread the center post and use a larger bolt or 2. use green lock tight Will these work? Is there an easier solution?

Thanks
Leeann