Need tips to get my lead to start using to TDD

Working on a legacy app which does 1000s of dollars of calculations every month but uses manual unit testing. I suggested to the team to use automated unit testing for future changes in the app using tSQLt. But there's pushback from the lead saying that it's hard to maintain the tests. I think this could be fixed by separation of concern. I'm planning to do a presentation with a few examples of how TDD would be useful. Please suggest some tips of help my present my case in a better way. The lead is kind of a Business Analyst/Backend dev.