Anyone knows where sell this medela rubber membrane/valve? It's an old model..preferably online so more convenient for me..

You can look through these: http://www.pupsikstudio.com/shop-by-brands/medela?product_type=6501 http://www.mumsandbabes.com.sg/index.php?option=com_virtuemart&page=shop.browse&manufacturer_id=4&Itemid=1&vmcchk=1&Itemid=2 Both shops carries replacement/spare pump parts for Medela. Hope the membrane you are looking for is in one of the lists. :)