What’s down there, and can it be repaired?
A friend’s D6B stopped steering to the left.  I had some ideas about what If might be, so agreed to have a look.  None of my ideas proved out, so I called in someone who knows more. 
it turns out that the lower anchor point for the yoke is (apparently) broken.  I couldn’t see it, but it feels like a cast bridge between two points, about 3/4 inch thick, and around 3” wide, maybe 6-8 inches long.  It’s a nice dozer, turbocharged, with recent track replacement, and runs great.  If the housing has to be replaced, the tractor would never pay off the cost of repairs.  
To someone who actually knows what’s in there, is it all part of the housing, and if so, can it be welded? 
I actually know a retired, highly qualified welder who is willing to take it on. 
 

cast can be welded or bronzed if done properly can last for years. the question is what cuased it to break in the first place.

Removed due to wrong info.

The lower yoke pivot point is a bracket with bushing welded in place. The steering clutch/bevel gear  housing is fabricated steel so welding is not a problem once you get access.
Here's a picture....
 
 

Thanks, Old Magnet, for the reply and the photo.  I think the owners have  the tech manual, so I will have a look at that in a day or so, and see what they want to do.  If welding is what it takes, if my friend Alan can’t do it, I don’t think there are many who can.