Is DexCom's business in trouble, or could this be a great buying opportunity for investors?A top healthcare stock to own over the years has been DexCom (DXCM 1.18%). The company makes continuous glucose monitors (CGMs) that help diabetics track their glucose levels. CGMs are necessary devices for many people, particularly those who have type 1 diabetes. And given the increasing number of people with diabetes in the world, investing in a company which makes these devices has generally proven to be a great in ...