I recently received a lamp like my Enchantress but the liquid did not close the air gap at the top after running for a few hours. The lamp I received was made in April 1987. I added some liquid of the same color from a similar lamp made in January 1987 to close the gap. The lava is cycling but only about 75% of the way up the globe. It stalls there and returns to the bottom. Has the specific gravity been changed by my modification? Is there any way to correct it?