If you're looking for a late 80s / definitely post 1990s jacket and you want a size smaller than your current 618, you might be best off looking for a 36 in a 118. Since that point in time, the basic pattern on both is the same, but the shell of a 118 is always one size bigger than the shell of a 618, thus a 42 in a 118 is equivalent to a 44 in a 618, a 40 a 42, a 38 a 40, and a 36 a 38. I.e. if the object is to size down one size, exchanging a 618 in a 40 for a 118 in a 38 will give you exactly the same size jacket nowadays - though of course the leather will be different.
If memory serves, the 118 is technically longer, but only by the sort of half inch that you'd never notice / is within the tolerance for any jacket in heavy leather anyhow. TBH, though, this is the first time I've heard of anyone finding a Schott sleeve too long: the more regular complaint is that they are on the short side.