The top of the trans has a seal where the shifter enters the transmission. Most likely yours is deteriorated.


To replace it you have to release a spring loaded lock ring below the seal, remove the shifter and separate the shifter halves.



I had trouble with the spring loaded lock ring and honestly didn't want to mess with trying to separate the shifter halves.
But since my seal was in desperate need of replacing I came up with a solution. I cut a bicycle inner tube to about 6", pulled it down over the shifter, stretched is over the base where the shifter enters the trans, and secured it with a couple of zip ties. The inner tube is flexible enough to move with the shifter, it only takes a couple minutes to replace, and I have enough inner tube to do a dozen more. Best of all it was free.
Click image for larger version. 

Name:	IMG_20171112_142230.jpg 
Views:	26 
Size:	117.3 KB 
ID:	14258
Click image for larger version. 

Name:	IMG_20171112_142225.jpg 
Views:	25 
Size:	77.2 KB 
ID:	14259