Extension roof ridge tied into main tiles

[stephenIsTired]

Hi Ive bought a converted bungalow that has a single extension with the roofs tied in. The ridge on the extension meets the main roof half way and previously it mortared together. There was leakage and Ive replaced the tiles on one side. Im wondering if there is a better way to join these than previous

 

[jj4091]

I prefer dry verges