Does Black Knot fungus affect Root stock?

Hi Folks
I have a Green Gage plum tree that has (mostly) succumbed to Black Knot Fungus. I have reluctantly decided to cut it down. There is a new side shoot growing out from the root stock and I was wondering if I could graft a new variety of yellow plum (don't know the exact variety) onto it, once the main stem of the tree is gone.
However, someone suggested to me that the root stock may already be affected. Not sure how I would tell.

Does anyone have this level of experience with Plum trees, root stock or Black Knot?  

Perhaps it's not a good idea to put a new plum in the same location as the old one. ...but it seemed a good idea to make use of the root stock since I need some for the yellow plum anyhow.

Hard to say.

In the wild, I have seen fruit trees (chokecherry) that are systemically infected with black knot, including the root stock. All new shoots are quickly covered with it.  

With my tame fruit trees, I have had good luck with a hard pruning to remove an infected branch. If I was forced to take out the whole tree, I would be skeptical about grafting onto a new shoot. But I think the only way to find out is to try.

Thanks for the reply Douglas. Well the Plum variety I want to graft on, is from a very old (at the tale end of it's life) Tree. I don't know if I'll get too many chances (or years) left to save this family variety. I will try multiple options to see what is successful. I don't want to risk it all on a previously diseased tree as root stock.