Plus WD-40 will wash right off the first time it gets wet.
If you need to lube your RA bushings, they're probably worn out.
And what a lot of people forget is that even new RA bushings can make the popping noises. Part of the TTB front end, they're all that way.
If you spray lube on rubber bushings, it will over time deteriorate the rubber faster.
If you have polys, they can usually survive lubing, and I would use white lithium grease because it's more waterproof. But there again, I don't think lubing them is the answer, if they are noisy it's because of 1 of 2 things: a) the bushings are worn out, or b) the bushings are fine but even new ones will make pop noises some.