Thanks for the comments guys. I agree that for the most part the stain is not too bad here and i might well leave it alone. But i do need to get the remnants of the cosmoline off, which you may or may not notice in these photos.
I am really curious about 2 things in regards to this keris. Firstly whether others (besides Rick and i) also see this as an older Bali form. It seems that many of the antique keris we see from this area are late 19th-early 20th, but this one seems older to me. I have not found nearly as much information of the Bali keris in this regard as, say, the Javanese keris, but this keris has features which are somewhat unlike most late 19th C examples i have seen.
Secondly i am really interested in when and why this (i presume) newer dress form developed. We have certainly all seen the cheaper examples of this sheath, but was it always intended for tourist sales or is there some kind of cultural origin to the form? As i remarked earlier, i have never seen any really old sarongs in this form so i would imagine it did not come about until sometime in the 20th century. This would possibly put such information into the living memory of some, unlike so many other aspects of the keris that have been lost to time.