The "L" stands for "low pitch" (or, in your case, "lucky" since you didn't know it was a low pitch horn when you bought it).  If it were marked "H" or "high pitch" it would be worthless.  Horns stopped being labeled with pitch designations some years ago, since no high pitch horns had been produced since before World War II.  So it's a safe bet that your horn is an oldie.


Selmer USA marketed the famous Selmer Paris horns and some horns produced in the USA by other manufacturers but sold under the Selmer brand, i.e. "stencil" horns.  Stencil horns were inexpensive horns for students and casual players, but they were often pretty decent horns.  They don't have a whole lot of market value, so it is quite easy for repairs to exceed the value of the horn if they need major work.  Enjoy your horn and keep your investment low.