I have a HB brewstation 40 cup pot. It will not dispense coffee, I think the filter at the exit spot is blocked. I have tried cleaning it with vinegar and a brush...but with little success. I hate to thow away the pot due to the malfunction of this little part. I have searched for a replacement part and can't find one like the one in the pot...one that screws in and prevents coffee from running out unless one depresses the dispenser valve. Where can I get a new part??