I have a 15 gal Aluminum. i have done boils, make turkey stock etc.
It will clean right up. Oxyclean was a good start. Trick there is not to do an overnight soak. Get a scotch pad and water and scrub all that white/grey stuff off the sides if there is any... and rinse a lot. You almost bring it back a little shiny.
Then to re season it.. fill it with water and boil it for like 10-15 min.. or whatever.. not sure on the time. You want a little grey on the sides... and this clean and re season will help with that.
When I have done turkey stock I have used http://picasaweb.google.com/lh/photo...eat=directlink
To clean the greasyness out. I will NEVER do that again - make stock - took a week to get my pot back.
But stay on it and you will bring it back.
Scrub, rinse, fill, boil, cool, dump water, inspect. If not clean (ie smells) then repeat.
That should do it.