I bought some Permatex White Lithium Grease (#80345) in a small squeeze tube from AutoZone. I applied some of it to every hinged joint under the spoiler I could find. I smeared it into the joints with a latex-gloved finger and wiped off the excess with a paper towel. So far, it seems to have fixed the problem. The spoiler made no noise the half-dozen times I raised and lowered it in the garage. I won't know for sure if the squeak is gone until I've driven it for a few days.