Howdy!
Lately my brake pedal has been squeaky. I haven't noticed any decrease in braking performance, so I think it may just need a little lubrication. Is WD-40 okay? Thanks in advance!

 

I take it you mean the squeak is coming from the pedal linkage... in that case any lubricant is ok. Just apply it carefully so it doesn't get into the booster (don't put on so much that it runs down the rod into the booster). Most booster diaphragms are EPDM and EPDM does not play nice with mineral oils.

To be more safe, I'd use a bit of silicone lubricant. And wipe down the parts when you're done so there aren't drips.

 

Thanks!