It's a common problem on those tractors.
The good news is it's not expensive to pull the upper part of the column and replace the upper seal - part # 44. Your dealer should have one in stock for about $13.
The bad news is it's an all day Saturday job to pull the tin off to get at it.
I generally replace the upper oring #32 while I'm in there too. Dealer should have that too for a couple of bucks.