The mistake is in overcooking goose, Fred. The meat does not have much fat in the muscle walls, so it has to be cooked in a wet environment, and you only want to cook it medium rare for best flavor, tenderness, and eating.
Before cooking it, you should soak it in cold water with either salt, or vinegar, to draw the blood out of the meat. That improves the taste to what we normally expect meat to taste. Otherwise, its too bloody and reminds our tongues of old liver, like the stuff we were served back in the 50s, in the public School cafeterias. Very Bitter tasting.
After drawing out the blood over a couple of hours, then soak the meat in CLEAN cold water to get rid of the salt or vinegar! Soak it for the same length of time. About as much blood will come out during this second soaking as did the first, but the end product is breast meat that looks more pink, than dark purple.
Use a good red wine, or some fruit juice if you can't or don't drink alcohol, to keep the meat moist during cooking. I suggest putting the meat in foil, with butter, seasonings, the wine, or juice, white onions, apples cut up, bell pepper or any other mild pepper to help flavor the meat, and then wrap the foil around the whole thing. The onion and apple, and wine or juice will help not only keep the meat moist, but help to sweeten it. The alcohol in the wine also marinates, and tenderizes the meat.
In fact, if you don't drink wine, marinate the meat in your refrigerator in a covered bowl, using wine as the marinade, along with any spices you like, for about 4 hours, before you cook the meat. If the meat is covered, and turned over at least once during that period, you should have a better tasting and more tender piece of meat to cook. Still cook it wet, but use water instead of the wine. What alcohol is in the meat will cook off during the baking process.
You can buy Plastic baking bags that will let you put the meat in them, with whatever fluids you like, and they can be used in the oven as their melting temperature is high enough they will not be affected by the heat in your oven.
I simply put mine on a roasting pan,with the water and wine in the bottom, and the entire meat above covered in foil, to keep the moisture in.
I have done these things cooking Canada Goose, which is also pretty tasty if smoked properly. However, I understand that White, and Blue Geese, much smaller birds that fly south later in the season, taste much more " muddy", because of where they feed, and what they eat. I recommend soaking these birds overnight, to draw out both blood and the muddy flavor. Then marinade them throughout the day to improve their flavor.
You can always use a pressure cooker to cook and tenderize old geese, BTW. Just put your favorite spices, or BBQ sauce in the Pressure cooker, and some water , per directions, and you will have a much more tender, and tasting old goose to eat.