Thank you all for your comments
The de-rusting went well:D the head came of pretty easy by turning it to break the glue, i only had to cut the last little bit of glue.
Butterscotch was pretty dirty inside, both washers were covered with a big layer of rust but luckily the clip was intact.
Oxi clean is great stuff, her body got clean AND brighter making the head/body mismatch even less visible
The only thing that went a bit wrong was the combing of the tail, i pulled out some of the hair:S luckely not TO much, i compared her tail with that of my FF blue belle and it looks oke.
FF butterscotch looks much beter now AND there will be no more rusting in the future:D