So, you find fault with my concluding that an 8-year old HDD should be replaced, tell me I'm not wrong about it, and then say we're actually agreed on this? Perfect. Got it.
Um, yes. We agree that you shouldn't replace the drive before determining what the actual fault is.
From what you've said so far I think you might be working on the assumption that the HDD is failing, and I also think that might be holding you back from identifying the underlying cause of the problem. (And performing any kind of disk repair on a computer with possibly bad RAM is, frankly, scary. Please don't do that.)
You don't like the way I look or something?
No, nothing like that, but I
have fixed a fair few MacBooks and others who've given advice in this thread have fixed a fair few more. If you don't even have the right screwdrivers then I guess you haven't worked on many of these yet (though I'm sure you'll correct me if I'm wrong).
I was trying to help by pointing out that you should at least try some of the very good advice given to you (replace the RAM) before focussing on something that is likely to be unrelated to the fault (an old but perfectly working HDD).
I also pointed out that even Apple says you don't need to remove the battery before replacing the RAM. It's a quick and easy test that will tell you a lot.
You asked for advice and you got it. It's up to you whether you follow it.
TL;DR - The symptoms are consistent with RAM failure leading to data corruption and it would be prudent to test for this before doing anything else. And that's all I'm going to say on the subject.
