What type of sealer should I use between the fender and the top of the inner fender?? Is it a seam sealer or a gasket??

Thanks in advance

My original sealer was something very similar to modern day duct seal(grey putty-like stuff that comes in a bar)so I used it instead. Got it at the hardware store. Main purpose was to keep out water/debris, so anything will technically work, as it was basically hidden.