I've replaced the valve and it's working great. For you that keep track of parts, the replacement was a Bendix E6, a dual brake system. It's identical to the original.
http://www.finditparts.com/t/1303/manufacturer/bendix/products/1488117/bendix-286171 (http://www.finditparts.com/t/1303/manufacturer/bendix/products/1488117/bendix-286171)
http://www.anythingtruck.com/Merchant2/merchant.mv?Screen=PROD&Category_Code=HTP-AIRB&Product_Code=061-286171X (http://www.anythingtruck.com/Merchant2/merchant.mv?Screen=PROD&Category_Code=HTP-AIRB&Product_Code=061-286171X)