Ive used that for 2 years now, never had any issues!
Issues can come if you dont seal the lid back on, since the CPU gets hot and cold all the time it draws tiny bits of moisture in, and that makes the LM "Corrode" the copper, but other than that, no problem doing it like he is doing!
EDIT: Gallium, which is a "ingredient" in LM, is actually made of small amounts of copper, and the same mix is used alot on solarcells, so, its not the copper`s fault, its moisture!