Personally, I would do it. Chances are, at 12,000 miles it has probably never been done, and I am not sure of the lubrication properties of lube that is approaching 30 years old. A couple hours spent getting into the drive shaft to look at it and put a little spline lube on it adds a lot to my peace of mind when far from home on a dark and stormy night.
My personal approach is to do a complete maintenance, fluid change, and inspection on a "new" bike. It finds a lot of "wow, I'm glad I found that" things the seller may, or may not, have known or mentioned when I bought it. Also, there are things like rubber bits that do not age well.