Lubrication

So now that I've got all of these beautiful used engines which I've been cleaning up I'm noticing some are a little loud. I'm sure that's the nature of these things but I'm wondering if they wouldn't benefit from a little lubrication on the main drive gear. I cleaned a good amount of oxidation off the batery terminals on several of them si I have a feeling they sa in someone's garage for a while. Anyway, I have white lithium grease which I've used on old Lionel engines. It's safe for plastic and I'd only put a little dab on. My only hesitation is that if they end up in the hands of children again Im not sure I want that grease there. Once again, I would only put a tiny amount on, but what do you think? Do you guys lubricate when you refurbish?