1986 Schlumberger GC Saering Riesling
thats a bit of a thinnish year in alsace, but the bottle in itself is a novelty... a 21 year old riesling. So give it a try, you have nothing to lose.
What I wouldn't do is fashion a really nice meal around this wine, only to find that it's seen better days. The best thing would be to prepare a riesling friendly meal (or get one at a restaurant), and BYOB this bottle in addition to some more predictable wines. If this wine is great, wonderful... if not you haven't had the meal for nothing.
Also, to the extent there's any life left in this, it will probably show better with a meal than on it's own, i'm guessing...