I can't offer any advice for your eel as I've never been through a situation like that with my eel. What I can say is even if they are picky eaters you should soak their food in multivitamins. When I first got my eel I noticed some weird things going on with him like really bad head twitching and lethargy. I started soaking food in vitamins and all his symptoms went away. I also only feed mine once every 3-4 days. I've been told if they are fed too much it can cause internal problems.I have tried a varied diet, but he wouldn't except much more then shrimp and he would insist on it every night I fed the fish, so you theory is definitely a good one.
I guess there is nothing I can do now but to make him comfortable right, this really has me upset as he was like my dog!