Not having done that myself Wilcom and probably stating the obvious remember the speedo drive retaining bolt is also the transmission breather so plugging the top port should keep that bolt clear. I also recall the one time I visited that area is the speedo drive bush and cable boot are inexpensive so if you need to sacrifice them it's no problem. Perhaps something as simple as a rubber grommet stretched over top and down below the boot lip, sealed with silicone will suffice?
