Hey smalldog, welcome to garden.org. Could you please fill in your personal profile with your location so we can have some clues as to your weather conditions, soil, humidity etc. It's the little person icon in the upper left of the blue sidebar.
That poor little sago looks really sad. Do you have any pictures of it before it fell ill? I'll venture some thoughts and then hopefully there will be more clues after we know where you are, and what the weather's been like.
First, it's very small for being 15 years old. I don't think this is a new problem, and it might be related to several factors. The very narrow planter bed there, between the house wall and the little retaining wall may have been leaching alkaline stuff from the concrete for years, keeping the soil at an unsuitable pH. Have you had the soil tested in their bed? How about your water? A high pH environment can make it so that plants literally can't access the nutrients in the soil. Hmm, how about fertilizer? What have you given them for fertilizer besides Magnesium sulphate in recent years? In a limited environment like that narrow planting bed
Second, It's also too narrow for the palms to have developed a full root system as they put out roots on all sides of the plant, a very dense mat in a circle around the stem.
Third, the fact that they've probably had increasing shade (as the nearby trees grew) in the 15 years they've lived there may have some bearing as well. These plants live happily in partial sun here in Florida, at least where I am. Plants can't make food for themselves without enough sunlight.
Any chance you've got a better place to transplant them to? Better soil, a little more root room, and more light might save them. But I'm not really optimistic.
