Oh faye, I'm so sorry! Magic Erasor can be fabulous but if overused, from what I learned from other PF'ers, it can be a nightmare! What I found worked on my Speedy 25 (it was a victim of "happy erasor" syndrome) was leather conditioner. I used Appleguard Leather conditioner. It restored some of the moisture on my handles and helped a bit.
However, it never got back to that original state so I've since sold it and will be buying a brand new one in Paris. I know that for some PF'ers who didn't go Magic Erasor happy using the conditioner helped ALOT.
By the way, where did you apply the magic erasor and how did it ruin your bag?