Why are people so concerned about the steel composition of their case? No one & I mean no one can tell the difference, visually, between the steel used to make a good rep 5513, 1680 or 1665 & the 316L Rolex used. In fact, with the possible exception of the brushed texture (which often looks better on reps), I cannot distinguish between my oldest, cheapest POS Sub rep case & my gens. Unless you plan to use your watch in an acid bath (in which case, 904L is definitely the way to go), I fail to see what all the hullabaloo over steel composition of rep/aftermarket cases is all about?
If you are talking about a modern Rolex, which uses the slightly whiter 904L steel, then you might have a point. But, even then, very few people could ID a rep case without having the gen on hand for a direct comparison. I certainly would never put any money on my ability to identify the steel composition of a vintage Rolex watch on the street.