Seat posts
Here are a couple of seat post images. All seat posts are the same but they are not.
The one on the right is original and from a 1916. The next (two from the right) is original and from a 1914. Three from the right is a good quality repop and the one on the left is a disappointing repop. The good thing is that the original ones are cheaper (!) but they are harder to find.
Look at the quality of the rivets location and fitting, and the shoulder step on the repop bodies.