Grease lasts longer & no risk of oil getting onto other parts if over oiled accidentally. I used silicone grease on my i2. Dielectric grease will also work fine if you have it on hand. I used Super Lube specifically as it's used in my Snap-On ratchets
The springs don't really need lube, you want to lube the sides of the slides, top & bottom. The issue is cause by the slides tilting when pulling back on them & the friction is on the plastic. Use a toothpick or paper clip to apply a few dabs along the plastic rails & work the slides back & forth. Mine are very smooth now & I haven't needed to regrease them yet after a couple months of daily use.