I've tried 2 digit and 1 digit transposes as well. No luck. So I believe I cut 3/4/5 consecutive digits somewhere and then inserted 3/4/5 other digits. The difference possible combinations start to explode towards infinity and I fear I've lost the coin forever. Does any recovery service exist to write code that tries to recreate all this possibilities? I know most of the private key, but do I know enough?
I wouldn't give up yet. You're only trying to find a standalone private key and one derived from some seed phrase, and this makes the programming task much easier.
I know some Python so I'll look for some old code of mine that creates a private key WIF from hex and I'll apply it to this problem.
Python is actually the right tool for this job given the extreme easiness to convert a arbitrary base to a number. You just take the string of digits as input and then pass it to int() along with the base. Most other languages don't have such a function so you'd waste some more time trying to write one.
Do you have a GPU? I have a feeling this search can be hardware-accelerated, and it's probably easier to write GPU code in Python than in C.