Does anyone know if the PH6811 has been discontinued or superceeded by the PH3593A? Considering the fact that it is nearly impossible to buy anything but Fram filters in Canada, and reading a few posts in here, the 6811 is a superior filter to the 3593. But a trip to my local wallmart the other night was fruitless - no 6811's in stock, and no stickers on the shelf to show that they exist anymore.