Tears of Guthix are 100% drops from any monster in the Guthix section in the God Wars Dungeon. The amount of tears gained depends on the NPC and is always the same. You can exchange these tears at Juna at the Tears of Guthix activity place. You can get experience, unique items or even Fist of Guthix tokens (in a rate of 1:10). You can also use them to buy time in the Tears of Guthix (in a rate of 10 Tears for 1 second).