Auk, i also agree with both you and Alan. Rescuing a neglected keris is a good deed in my book and i think the only people who will receive "bad luck" from such a kindness are those that convince themselves that it's true and manifest it in their own minds. Belief is a funny thing that way.
I also don't see your keris as being particularly "broken", though to does have some condition issues for sure. Some of that is to be expected with an older keris. I am having a hard time understanding why Tunggulametung thinks this is a late 20 century keris. Seems just a bit older than that to me at least.
On the question of fitting a pendok, this is just my personal opinion. Many people who collect keris feel the need to change and upgrade the pieces they own. For me i am collecting a piece of ethnographic history and i am more interested in maintaining, preserving, conserving the object and trying to understand it in its original context. If a mendak or pendok is missing or broken i might replace it. But this sheath was obviously made for this keris. It is wrongko iras which is a bit rare and much harder to make. I don't believe this sheath was ever intended to have a pendok. IMHO, fitting it with a pendok now would be incorrect and in order to do so you would probably have top do damage to the gander in order to fit a pendok over it. That makes no sense to me.