BMW forgot to tell me they were closed for stock-taking today so I couldnt get the microfilter. Finished dismantling the tranny instead. Hadnt found anything wrong so far and the 3 machine screws that hold in the D/G clutches were proving akward. Once out all was clear - the spring ring in the D/G had disintegrated and 'shaved' the castellations off the top of the F clutch. Chunks were also embedded in between the clutch plates. Plates in the F clutch seemed a bit loose apart from that the tranny is fine....