"Several years ago, I bought a set of decals for a Delta Air Lines DC-9 from an individual who advertised them on the internet (on an airliner modeler's forum ... I don't recall the exact web site).  I bought the decals to finish a blank polished aluminum 1/50 scale DC-9-14 model that was produced by the Douglas Aircraft model shop.  I never got around to tackling the project until this year.  According to the information on the decal sheet, they were printed in 1971 by the Douglas Aircraft model shop.  I have never seen another set like them (original Douglas model shop prints) advertised anywhere since I bought mine.  The decals were very difficult to work with, as you might expect due to their age. 
Before I even attempted to remove the decals from the printed sheet, I applied three coats of Microscales's Liquid Decal Film.  Then I used copious amounts of Micro Set and Micro Sol to apply the decals to the aircraft.  Even with using these Microscale products, the decals split apart several times while I was applying them due to their age. 
Fortunately, the Microset and Microsol allowed me to reposition all the pieces and I was able to fit everything together so that you can't tell that the decals were ever split.  I could never have used the decals without your great products!"