300D Turbo vacum problems

[shoe]

Can the vacum pump on my 83 300D-T go out a little at a time? It seems to be making vacum intermitantly, I pulled the line off at the brake booster put my thumb over it, had fair vacum, raised the RPM to about 2 grand the vacum went away. I then disconected the plastic line at the vacum pump had great vacum, reconnected at pump rechecked at brake booster had great vacum that time, raised RPM again everthing OK now.
Should I look into rebuilding the vacum pump? If so does the partshop stock what I need?

------------------
Keith Schuster
99 Harley Davidson Ultra Classic
97 Dodge Ram
83 300D
auto\hydraulic mechanic 20 yrs