Tamanaha Seikichi Oil Painting of "Old Mother"

This is a oil painting by Tamanaha Seichiki, painted in 1953. Tamanaha Seichiki was a member of an artists colony on Okinawa -- the Okinawan artists of the Nishimui Artists Society. I believe this painting was a study done in preparation for a larger painting done by Tamanaha in 1954, titled Portrait of Old Mother. I was able to view that painting on a website about the arts of Okinawa. I am quite certain the woman sitting for that painting is the very same in the painting that I own. The painting is done in an impressionistic style with very thick paint. There are areas on the surface of the paint where it has cracked and there are 2-3 small places where the canvas has been "bumped" and there is additional cracking to the paint in those areas (in the background and on her robe). There are no holes or rips in the canvas. Right now at UC Berkeley there is an exhibition of these artists, and I learned more about this group of artists from their show information. I am having a very difficult time finding out what my painting might be worth. I believe it is an important piece of Okinawan history. Thank you for any help you can give me.