It is not WIF.

Like in PM.

What I would try

Before next step:
Do another offline copy of https://www.bitaddress.org/

Play:
In https://brainwalletx.github.io/#converter paste you 53 char - (Convert to HEX) - copy every HEX, from every available source encoding.

Go to saved, offline www.bitaddress.org -> Wallet Details -> paste saved HEX to Enter Private Key -> View Details.