I was driving down the highway in my 1990 defender 90 200tdi. I was at about 55-65 mph for 22 miles and all of a sudden it squealed and then smoke came out. Feeling like it came from the trans as I have a lot of oil coming from it more than I had before. Before I had a couple leaks but nothing to worry about. This smells like it burnt the clutch but a tiny squeal sound when going in reverse and forward for a couple feet. I can still drive on it as I did for 5 miles after it happened to get to my destination. I have no idea what it could be or if it's safe to drive. Please help.