Can you tell me what the most often revived musical is in Broadway history. I am asking about Broadway revivals not productions around the country or touring productions.

This is a very difficult question to answer - it is not cut and dry. There are many factors to consider, including some theaters that were once considered "broadway" theaters, but are no long. In the 50s & 60s the summer theater at Jones Beach on Long Island was considered Boadway, which now seems ridiculous. Also, the City Center is now considered a Broadway theater, but didn't used to be.

It is believed that The Mikado is has been revived on Broadway 28 time. However, while this is a musical performance, it is not considered "a broadway musical".
Showboat was on broadway 8 times. Many people argue that this would be the most revived musical

I agree. Very difficult question. Have you tried the following search?

Broadway Musical Revival - Google Search