Two years ago, I was diagnosed with MS. I lost all fine motor control and most of my short-term (and some long-term) memory for a while (funny, but I don't remember how long... ). Most of it's back, and I'm playing (piano, mostly) for barndances again and having a most wonderful time. Technically, my playing will never be what it once was, but I'm a much better musician now because I'm so utterly joyful to be able to play that I don't care about any of the self-focus stuff that used to get in the way of The Music. What a blessing!

To answer the original question, however: I have lots of problems learning new lyrics now and have pretty much given up on memorization of anything classical, but the old stuff comes back freely, most of the time. What I learned before I got sick, I still have. Weird. Wonderful!