Well in the meantime we should understand if the seed is 12 or 24.
OP is talking about a private key and that's different from a seed phrase.
Th most common format of a private key is WIF and that includes 51 or 52 characters. Even if the private key OP is trying to find is a mini-private key, it would include 22 or 30 characters and as mentioned by mocacinno and LoyceV, that can't be brute-forced.
oh fuck...i didn't read private key and my mind automatically deduced that it was a pass phrase...you're damn right. So here things change a bit and only prayer remains as an option.