Weld seams on quarter panels visible in hot sun, but not garage--how to remedy?

[yellowrallys]

Wow, I had the EXACT same thing going on on my Camaro. (black in that area) I originally stripped the car and tiptoed around the original lead joint, trying not to disturb them. (did not replace quarters) I was thinking the factory joints would be okay. After a while, I noticed the seams showing when hot, in the sun, after cooling they would go away. So I dug all of the lead out, welded the seams solid, epoxied, and went back with a dynaglass type filler and repainted. It was worse than before. SOOO...I dug it all back out again, down to the weld. I epoxied again and went back with only Rage Extreme and so far I haven't notice anything. You might say I tried what everybody including myself thought was the right thing, then ended up doing the simplest route.