I've lubed the cores of five cubes so far.
In each case, I lubed the spring ends contact points ( screw head underside and base of cenre piece ) plus the washer if present.
I used the tiniest amount to only the core.
It's messy but I just was careful and it cleans off the cube with a cloth easily, especially with a single drop of cube lube on the cloth.
MoYu RS3 M 2020 :
Magnificent cube to begin although one spring was nousy. Core spun much more freely after applying Lubicle Black. Completely removed spring noise from the cube also in this case.
MoYu Meilong budget 3x3x3 : love this cube and sometimes prefer it to my RS3M as it's so smooth anyway out if the box. After Blacking the core, it turned even better noticeably.
'Twisty Puzzle' imported bandage kit cube :
Cube itself was very dry and hard to turn. When strippef, the core was poor to turn. After Blacking, it spun like a dream! Had to lube the cube runners and edges with regular Speedy also and this cheap, gratey cube now feels premium quality and turns lovely.
QiYi (box said Yong Jun) Warrior S:
Beautiful budget already turned incredibly well out of the box, but after Black on the core, it was even more speedy.
"Roxenda' ( unknown actual brand ) super-budget cube:
Core went from stiff turning to free-spin after Black.
Good stuff