Welcome to the forum Peter.
I will wait for others to comment on some of your details here. I will pass on a saying we use around here often though. Buy the keris, not the story.
I would not get too attached to the idea that this is somehow a keris connected to the keraton, for instance. The use of scented oil on keris is quite common and does not necessarily indicate such any such connection. Keris salesman in Indonesia will attach many different tales to their wares to boost their sales. What you do certainly have here is an authentically old keris. I sincerely doubt, however, that anyone can pinpoint the date of such an old keris to an 18 year period of time.
Better photos would be nice for better identification. It appears to me that your wrongko was once a ladrang style that has been greatly reshaped, probably due to damage to the original form.
I look forward to seeing your keris singo, but would not hold on to the hope that it has used pamor from the Prambanan meteorite. Such material was reserved for truly high level court pieces. If indeed you have one of those you are a lucky man.