Hi Tim: I'm a little confused. You say "All of the contracters said the same thing; install new sub-floor lay over that, so we did that. Now the problem has returned?" Does this mean that you had the contractor install a new subfloor over the old linoleum, then a new linoleum over than, and the stain returned? If so, this is truly puzzling! A GRAPE stain? Does it have an odor? For an existing stain to rise up through a new subfloor and through a new linoleum floor would require lots of hydrostatic pressure....lots of it. The most likely explanation is that you have a moisture leak somewhere that is also carrying with it some kind of dissolved substance. Is it near your refrigerator or dishwasher? Can you see the stained subfloor from underneath (basement or crawl space)? Localizing the source of this stain will be necessary before you can do any repairs. Otherwise, it will just keep coming back.