One of the forum members (Luis) recently found a source of the square cross-section O-rings used on the oil filter case. At only $.49 (U.S.) each, they are very inexpensive. The link is: http://www.theoringstore.com/index.php?main_page=product_info&cPath=2203_98_100&products_id=4341
You can cut/paste the like above in your browser URL line.