Handy Jellies, can you help me fix this?

There is a hairline crack in the tank of a toilet in my house that is slow-leaking. Can anyone recommend a product that I can use to repair it? It would only be a temporary solution, for a few months. Is there a sort of rubber seal type thing that will work? I have discovered, that in spite of all the hype, duct tape does not cure everything. Damn