Help identifying the location of a leak in a block wall.?

I have a cinder block wall. Block is two cell 16x8x8. Outside is stucco and has been painted. The wall is 24' by 10' and is the side wall for the garage. on top of the wall is the 1st floor of the home and is frame with red brick exterior. Above is the roof peak which is vinyl siding. The siding has been replaced by a professional. The leak existed before the new siding as well. Most times when it rains there is no issue, however when the rain hits that wall directly, i get moisture in my garage but only in a certain area about a foot wide. This is not condensation. as it only happens when it rains and then only when it hits that wall.

Can anyone provide any tips on the best way to identify the leak? What kind of professional would be best to call?

Thanks in advance.