Wiped down left tank skin and ribs 1 & 4 with MEK. Clamped rib 1 in vise. Placed Proseal on skin's rib line and rib 1's flanges. Wiped off tails of rivets prior to riveting. Clamped rib 4 in vise. Placed Proseal on skin's rib line and rib 4's flanges. Riveted rib 4 in place. The rivet in top LE position did not sit properly in the dimple, so it was drilled out. Placed a 3-3 rivet in its place and riveted. Wiped off excess Proseal on outside tank surfaces with MEK. Cleaned off all clecoes. Made about 40 grams of Proseal.