It's one of 240 "Last Edition" models made before BMW changed its mind.
In an alternate 1984, BMW would have discontinued all of its air-cooled motorcycles. It was the end of the road for all of BMW's big boxers, from the R100 to the R100RT. They'd had a good run since their introduction in 1976, but to keep up technologically with the Japanese, who were switching to water-cooled engines, it was time for BMW to do the same and switch to the K100. The 740 "Last Edition" models, including 240 R100RTs, would be the end.
That's how it was supposed to work in our own timeline as well. However, due to massive objections by owners and dealers alike, the BMW R100RT alone was given a 12-year stay of execution, remaining in production all the way until 1996 with continuing improvements along the way. Choose your science fiction time-traveling franchise of choice, and perhaps Marty McFly, the Doctor, or even Bill and Ted traveled to 1984 to convince BMW executives as well. It wasn't supposed to be this way, though, as the extensive documentation provided with this now inappropriately named R100RT Last Edition on Bring a Trailer shows.
Gallery: 1984 BMW R100RT Last Edition
BMW pulled out all the stops for this one since it was supposed to be the last. It has unique paint, pinstriping, and definitive "Last Edition" lettering above the model name on the side covers. It came with hard saddlebags, a clock, a voltmeter, and a pair of seats to use depending on whether you were riding solo or with a passenger. Advertisements of the time made a point about how valuable recently discontinued BMWs have become, and promised that this would be one of them because there would be no more 1,000cc air-cooled flat-fours.
That is, until there were. Imagine how angry the people who bought theirs to preserve as collector items were when BMW decided to go on making the R100RT anyway. Still, being one of 240 is still pretty rare. The seller of this one has owned it for the past 30 years. It has just 18,000 miles, only 6,000 of which were added by the seller. Time travel to our present-day and this R100RT Last Edition finally fulfills BMW's promises. While it wasn't truly the last R100RT, it's a well-preserved example that is, once again, rare and collectible.