When lubing plastic, you want to be really sure that the lube does not damage the plastic in the long run. That means that the lube must be absolutely free from any solvents that could damage the plastic.
The composition of WD-40 is a trade-secret, but it is likely that it could contain solvents that are bad for your keyboard.
People around here use either:
- EliteKeyboards'
MechLube for stabilisers[/url] and
MechLube-2 for switches.
- RO-59KT, which is a PTFE ("Teflon")- based lube, once made for Key Tronic. Best for the stems of linear switches, not so much for stabilisers.
- Krytox. There are several variants. Usually Krytox GPL206 for stabilisers and a mix of GPL206 and VPF1506 for switches.
The latter two can be acquired in group orders now and then.