Rolex 6426 crown and tube advice needed

[Newboy]

I’m new to this forum today, so I apologise In advanced if my terminology isn’t correct but I’ll try my best.

I have my fathers 1970s Rolex 6426 oyster precision. It’s running ok but the crown won’t screw in, looking on a few YouTube videos I think it’s the crown thread worn, or the crown tube I think it’s called.

I feel it’s something I could take on. Just wondering if anyone could tell me what size crown and tube I would need. And where I can the parts?

I was planning on removing the case back first and removing the crown, I think it’s one screw to release the crown?

If it’s the crown tube would I be right in saying there are two or 3 screws to undue to remove the movement, then I would use an extractor to remove the tube. Any idea on what size extractor to buy? Also it looks like it could have had lock tight on. Are the tubes easy enough to remove and replace. And would this model have an o ring or seal.

Also is there an easy way to determine what part needs replacing or is it just by eye. I was thinking of purchasing the cheapest part the tube, so I can test the crowns thread on the new one. Any advice help would be much appreciated.

Chris