Blockchain wallet uses BIP39 so in addition to what you wrote in the 5th point, OP has to go to 'Options' and check 'BIP39' before clicking next:

Or you could export the wallet.aes.json backup and decrypt it, you will find xpriv which is the master key.
Wallet.aes.json? Didn't they stop allowing users to export their wallets a few years back when they upgraded?