Thanks. The gap is less than 1/8", so I don't think we need backer rod. Just caulk and paint. The black gunk is making it look like a wider gap.

I would just live with it. It's hardly noticeable. You could easily make things worse.

The black gunk might just be the plastic wrap that was used to protect the stainless during shipment and installation. I have some of that on my large outdoor grill and hood. I would try stainless cleaner on the black gunk and maybe scraping very carefully with a 2-sided razor blade. I wouldn't use sandpaper on the stainless.

Would you consider moving the recessed lights? Looks like they got placed too close to the hood and are giving you lots of glare.

Thanks chispa and party_music. The black stuff is a slightly oily goop that wipes up very easily from the steel surface. It's just going to be a pain cleaning it out of that gap. And yes, we need to fix the recessed lights. The glare is super annoying. But we're going to leave that for a few months, until we're ready to tackle another set of needed electrical upgrades. It's time for a break on construction.

Agree with others, esp @party_music50 that before cleaning "goop" you need to know what it is. You need to know that, so that you know which type of solvent to use. There are plenty.

Ask the contractor what it is! Once you have a brand-name, you can call the company that makes it and ask how to remove it. Once you have a brand-name, you can research what the goop's properties are and therefore discern which products will be useful in cleaning.