OK, the basics:
You should have enough backup copies of your original wallet file, so that you won't ever loose the original.
You never work with the original, you work on copies of a copy of your original wallet file. Key is to never ever modify the original.
You work in a safe environment which in most cases won't need a network connection. You don't want to foolishly loose your wallet file to some hacker, even when it is still encrypted.
Your wallet file copies have to stay away from online devices of which you're not sure how safe they are.
Temporarily turning off the network doesn't make a device persistently safe. A compromised device can still leak data later once a network connection is re-established.
Document every step and recovery attempt so you don't loose track what you already tried.
I would very highly recommend to test your recovery tools with a self-created encrypted wallet which encryption passphrase you know. Just pretend you don't know it and give the passphrase generator better hints so you don't spend too much time to test. Evaluate your toolchain from start to finish with your sample wallet as if it were the real wallet to crack (begin with hash extraction, because if you mess up already here, nothing will work later).
If you can't find the solution for the sample wallet, it's not likely you would find it with your real target wallet.
It's mine. I don't remember the passwords from that time; I change them regularly. They're less than 12 characters.
Write down anything you remember how you created your passwords. Many people stick to a certain composition scheme. Relax and don't try too hard, this blocks your head. You're not in a hurry, I assume, so take your time.
Less than 12 characters sounds like doable, if you have some reasonable hints for rules for the password/wordlist generator. Of course it depends on how you composed your passwords in that time.
I don't know why I didn't think to make a backup at the time.
Human memory is fragile, especially if you don't refresh it regularly by repetition and use. What I menat with my question was, why didn't you write down your password? What made you think you could remember it indefinitely? Your and numerous other cases proved, people will forget their secrets, it's almost inevitable.
I have very own experience with forgetting passwords and passphrases which I thought I won't forget. I even had written down some hints, but seem to have introduced something new which I couldn't remember, foolish me...
That wasn't a nice experience, rather embarrassing. Now I document and write down anything or store it in password managers with enough backups so a total loss is quite unlikely.
It makes me wonder if a password leak might help me.
I have no idea what you mean by that. Frome where should or could your wallet encryption secret leak?
