I baked some potatoes the other night and while I thought to put a sheet pan underneath them, I didn’t think to put some foil on it, and now I’ve got little puddles of vegetable oil baked quite solidly onto my sheet pan.
Any recommendations for cleaning? It’s already been through the dishwasher once, though not on pot-scrubber mode.
Magic Eraser.
Although, I let me baking sheets get covered with grease and oil - it makes it into a non stick surface like seasoning a wok or something.
I don’t think I want to take cooking advice from you. 
Pick your poison and decide how much elbow grease you want to use vs how much chemistry you want to use:
Magic Erasers
Brillo
Carbon Off (this is a commercial product available at restaurant supply shops)
Non-stick surface? Our aluminum “non-stick” baking sheets just become cruddy, unevenly-surfaced, and super-sticky after a time. What materials are your baking sheets made of?
Part of what irks my organs about this situation is that this is one of the two new half-sheet pans I just bought on my inaugural visit to a real restaurant supply company. Awesome, hefty pans that cost me half what they would have at Bloodbath and Beyond.
I’ll definitely grab a magic eraser while I’m at Target tonight. Thanks!
Hate to burst your bubble, but that’s what’s going to happen over time. Personally, I don’t find it worth the effort to make then sparkle. I’ll scrub off the crud, to be sure, but I don’t worry if they are brown-ish, cause in the long wrong there’s no way to stop it from happening.
Try squirting full-strength dishwashing liquid on it, spread it over all the sticky parts with a paper towel, and let it sit for a few hours. Then scrub.
I didn’t know this was going to be a controversial idea. 
And now that I think of it, I think my sheet pans are just plain old steel (like a wok or a dutch oven or something), not aluminum. I have had them for over 10 years and they are very dark brown to black now and very little sticks to them.
I guess this won’t work for aluminum though - different physical properties.
By the way, I find the magic eraser is the best for cleaning up stuck on grease and oil. I use them primarily on my backsplash/stove control panel, burner pans, and the side of my fridge which sits close to the stove top… anywhere that gets splattered with oil when I pan or deep fry.
Baking soda & elbow grease usually work like a charm on caked-on grease for me. Get the thing wet (damp, but not much pooling water in it), add some baking soda to the pan so it makes a paste, and scrub.
Oh, I know. But these aren’t even two weeks old! 
Worth a try and effectively free. One less thing to buy.