If the keys are sticky due to a liquid spill, then you will need to have the laptop repaired. With an official Apple repair, it will be expensive to have the Top Case/Keyboard Assembly replaced. Plus a liquid spill may have damaged other internal components even if the laptop appears to otherwise be functioning fine.
For the laptops I support for my organization, I will remove the affected key caps & scissor mechanisms to clean the liquid residue from them and the key bay itself. I will only do this if only a small number of keys are affected since it is a risky & painstaking process since it is very easy to damage the key cap & scissor mechanism when removing & reinstalling them. I do not recommend you to do this yourself since it is very easy to damage them, plus you need to know exactly how each affected key is attached in order to remove it properly (the process can vary due to regional variations of the keyboard since Apple does source components from more than one manufacturer). The longer keys keys are even worse since some may have two scissor mechanisms and even stabilizer bars. Perhaps an Apple Authorized Service Provider would be willing to remove & clean a small number of those keys assuming they don't need to address any other internal liquid damage.
