Home inspector told me we have to put some new kind of 'glue' on tiles?

If the roof was replaced/built according to code in 1999 and is still in good shape you do not have to upgrade to adhere to the new code. If the roof has to be replaced it would fall under the new code. It sounds like it does not have to be replaced and you have done all the necessary repairs and would not be required to update your roof.