I assume you used K-meta when you made the wine. It would have been included in the kit as an addition late in the process. When I age wine for an extended period in a carboy or demijohn, I will typically add 1/4 teaspoon per 6 gallons of wine every 3 to 4 months. I will note that I have never kept a wine for 5 years in a carboy. I usually age my whites for about 6 months and reds 12 to 18 months.
I only asked about the airlock because I was looking for a way air could have penetrated. I always use an air lock (again, for a shorter period than you did) because I am concerned about barometric pressure changes that could force a solid stopper out of the vessel. I would have bottled the wine, at the latest, after 18 months in the carboy.
I am sorry for your bad experience. The important thing is to learn from it.