I think it's highly unlikely that Selden grease is unique. It's handy to use, as it's in a small plastic tube, but I'm sure that any similar grease would be just as good.
No, nothing special. The old blue tubes with brown grease were calcium grease. I think the newer white tubes are silicone grease. Either is fine. Ideally get one that doesn't liquify and run out in hot weather (since it says Leros on your blurb).