My friend's 740 GLE has an odd problem with the overdrive, you engage it and it clicks in immediatly, but when you press the button to disengage it the dash indicator goes out but the OD stays in gear, you can even downshift with it still in OD, eventually at a random time it disengages with a somewhat unhealthy sound. It never seems to slip though, is this something that can be fixed or should we grab a new tranny from a junkyard?