there may be trouble ahead...

[Dead Eye]

Any sort of strong degreaser should be a good start. I tend to use Ultra Gunk which isn't too bad, but I've taken to using the Muc Off Chain Cleaner for most hard to tackle jobs as it seems to just eat through anything - use it at your own perile, this is not advice, it's just what I do. Can't say for sure if I should be using it so usual internet disclaimer...