When they paneled my house, I asked the builders if water would get into the siding joints. They assured me that no.
As a result, when the snow melted, water started flowing in behind the siding at the basement. I turned to the builders with a request to eliminate, since another warranty under the contract is that they told me that I had the house srank on the 3 cm. The house has been under heating for three years and there were no other apparent causes of shrinkage.In general, they do not want to fix and recommend waiting another year. And a year later the warranty will expire.
I decided to write them an official complaint, but I do not know how to describe this defect in a claim and refer to any technological standards.
Fill it with sealant and you're good to go.
Buy a small white sill at the market. Remove the bottom slat of the top siding (or 2 slats, just enough room for your hands). Glue this sill to the main wall to completely eliminate moisture flow from the top down. The outlet of the sill should completely overlap the bottom siding.
There is no need to seal the gap between the bottom siding and the sill.
In my case, the joint between the metal siding and the plinth has a metal drip edge. They make any width and color to order. As I understand in your case, it is the best option.
In your case, remove the siding, take pictures and send a claim that the joint is not airtight. Or waterproof yourself. Sealant is inexpensive.
If the plinth protrudes outward at the junction with the main facade of the building, install the sill. Your photo does not show the connection of the plinth to the main facade very well, but you can see that there is no sill.