rocker panels on '68 dart GT

Can somebody tell me that where the rocker panel meets the rear quarter on my '68 GT, did the factory have a lead fill to connect the two, because Im cleaning it up to install new quarters and at that point I started to cut some of the rocker and..... no sparks, almost like a silver solder for about 3-4 inches, what gives, and if so I guess Ill have to cut more rocker out and replace, the rockers are Mint on this thing.