I have not played for that long and I have tried to learn the intro solo to Fade to Black which is quite hard to play for me. I am still learning that fast part around the frets 15-19. The only way to learn it is to keep playing it over and over again. But the problem is that when you play the same few notes all the time you get sick of hearing them and you don't like that solo anymore. Is this common?
Yeah, I get fixated on things, and by the time I can do them I've lost interest. You end up looking for new challenges instead of playing music - lotsa technique, no tunes. Try something different for a bit and then go back to it?
I'm working on the same song as you, and it does get tedious and frustrating. I decided to learn Master Of Puppets, and I go back to Fade to Black every other practice day and I find it keeps it fresh for me.