Learning hard songs by ear

I am trying to take my technique to the higher advanced level at this point so i started learning difficult solos. Difficult for me is up at Clapton, marcus king, Srv, buddy guy, etc. What would be advised to have mastered before attacking these kind of songs. It seems that just listening to loops of parts of the song is pretty inefficient and ultimately ineffective. Also, how would you or how did you go about learning the hardest song that you know?

This is an important topic. 

I start by identifying the key. It it’s F# minor I start playing the boxes. Because I don’t have an ear, I have to do it note for note, 1 bar at a time. I am currently transcribing Lazy by Deep Purple. 

That is very impressive Bill. Not something I am able to do. Also great tune!!!