The wine is Le Montrachet 1978, Louis Latour. It has been stored properly since shortly after release, and there were no cork, fill, or other issues. If I remember correctly, during this era Latour and another grower traded some wine to increase the variety that was offered by each, and this Latour Montrachet is the result of that trade. While not as famous as the likes of DRC (and less expensive) I have tasted several older bottles of Louis Latour that are quited good and that have lasted well.
The wine is bright and has a light lemon color (no brown). It has developed much complexity with age. There is still typical fruit, but there also is a complex mixture of waxy, honeycomb character with hints of nuts. Also there is a bit of mineral character. Although completely dry, the texture is nearly that of a late harvest sweet wine. The extract seems to be very high. Clean acidity is well balanced against the large body and reasonable alcohol content. The aftertaste is long.
I don't know what has gone wrong with many "top" white burgundy wines in more recent years, but it has to be something to do with making or bottling of the wine. Many top white Burgundy wines. and not just Montrachet, from the 1980s and older could easily last over 30 years if properly stored. Many of these older wines were not very user friendly before at least 10 years, and likely had a considerably higher sulfur content than is usual now.