Re:  "master private keys"   "x1/"    then a  very long string about 1.5 times the length of an xpub key, with '/', '+' and '=' symbols. The letters 'xprv' are not in the key strings between these (long and short) anywhere

This encrypted key is now un-encrypted, and begins xprv. However, it is just 'x1/' there is no 'x2/' showing