I don't personally have any good sources for how to troubleshoot connection leaks. They can happen in the front-end or in SQL code (usually because of not closing connections when using sp_OA* code). Connection leaks are very difficult to find.

Hopefully, someone else will have some good articles on the subject they can point us to. I haven't looked at the articles themselves, but there seems to be a decent selection of articles on the subject if you Google for "troubleshoot connection leaks" once you filter out the plumbing problems. 😀