Greg; it would sure be nice to figure out what's causing the demise of this three year old plum..? It would be a shame to propagate it, only to watch it die yet again... do you have any idea what variety it is? Occasionally, if not usually
people have a well known variety and would be best off tracking down a virus free replacement.
But if you're intent on continuing its line â€¦ how 'fast' is it dying? Does every branch look equally bad, or is there a 'good one?' If you've got a still-healthy branch, or 'water shoot' you can / should allow it to develop as long as possible before removing and Budding (Bud-grafting) it to another tree or rootstock later this summer. ...up here Summer's just begging...
If the tree looks equally bad, as far as grafting, your only hope is that at the base of its new leaves the buds have developed enough to be transferred (Budded) to the rootstock you mentioned. And this rootstock needs to be very young, 1 to 3 years old, with bark thin enough to allow you to delicately transfer a bud or two from your ailing specimen.
Here's a basic site on "Budding Techniques":
http://www.ext.nodak.edu/county/cass/ho ... ft/bud.htm
Here's a site with great photos, just click on one to enlarge it. It applies to citrus
, but I think it'll work for your plum:
Home Fruit Production-T-Budding Citrus Julian W. Sauls, Ph.D.
http://aggie-horticulture.tamu.edu/citr ... udding.htm