I use WD-40 for cleaning stuff and sometimes in machining certain alloys. I buy it in 1 gallon cans. But I don't consider it a lubricant. If you want a thin lubricant, try
Kroil - which is also a superior penetrant. Kroil is in the "magic" category for many applications.
Ordinary carbon steel blades that might be used with food stuffs may be safely protected and lubricated with pure mineral oil (pharmacy section of your local stores). There are USDA-approved food grade lubricants (usually silicone based *I think*), but I have not tried any of those. You could try mineral oil on your Leatherman, but read on...
IMO the leathermans are what I consider a "sticky" alloy - it may be the alloy or the hardness or a combination of both, but if the Leathermans we own were firearms or powered machinery, I predict that we would have constant galling problems. So you might want to look at anti-galling type lubricants - these tend to be synthetic thin greases, usually with a micro suspension of PTFE ("Teflon"). One that I am personally familiar with and can recommend is
Tetra® Gun grease.
You can also try moly disulfide treatment. I have it powdered, suspended in a volatile carier, and as a suspension in various oils and greases. It only takes a little bit, but it's pretty darned messy getting rid of the surplus! Moly adheres to both surfaces and dramatically reduces friction. By itself it is NOT a protectant and may even cause stainless steel to pit underneath the moly layer, so be sure to use a rust preventative oil or grease after treating with pure moly.
Action Lube Plus is an example of a moly-containing grease.
Don't want to go to a gun store? Get a quart of automatic transmission fluid from whereever you purchase automotive oils - that's a pretty good thin lubricant at a bargain price. If you need it even thinner to penetrate tiny crevaces, thin it up to 50-50 with mineral spirits - the solvent will help carry it in and then evaporate.
Or, as previously mentioned, sewing machine oil or 3-in-1 oil are good as well.
WD-40? Use it to flush out any gunk in the Leatherman, but don't expect it to really lubricate or protect the tool.
Lots of better choices than WD-40.
HTH,
Tom