My 1987 560 SEL (156K miles) has a bad transmission leak that does not appear to be coming from the pan gasket or the front seal. Instead it is coming from the right side of the transmission from the unit that looks like some type of transmission governer. The leak seems to be originating from an inaccesable plug toward the top of the unit. Any idea what this plug is and to get repaired? I have to add transmission fluid almost on a weekly basis.