Actually that is not entirely true, the Aurora shuttle has only ever been offered by Aurora. Airfix did an Orion shuttle was their own unique mold. Moebius did a new version of the Aurora kit at the same size with the same parts layout, but they corrected a few things on it, such as the angles of the grid patterns on the wings and added a couple smaller missing details. To my knowledge, Lindberg never reissued this as it was Monogram who got the Aurora molds after Aurora folded. But Monogram never reissued the Orion in their packaging.
The original 1968 issue Orion shuttle from Aurora is unique in that it has two bands around the fuselage and tail which feature a roughened texture (painted in a darker color on the instructions). When the model was reissued in the early 1970s with the Robert McCall style box art featuring the Orion blasting out of Space Station 5's docking bay, those rough texture bands were made smooth instead. This makes the earlier kit potentially a little more desirable to collectors. You can build it or sell it, although it might be best to get a Moebius Orion shuttle and build that (Pan Am decals are available via aftermarket sources) while saving the 1968 issue for keeping as is or selling. But if the kit has water damage, that might affect how much you can get for it.