Watching this vid, how I'd improve on this: YouTube

I didn't notice a gasket on my 4runner when I pulled the OEM rack. Perhaps it was stuck to something. In the event that there is a gasket, this is what i'd do.

1) I'm anal so I'd use butyl rubber as described earlier in the thread around the OEM spacers
2) I'd also lay down several thin strips of butyl underneath the rubber gasket (directly on top of the paint) as well as around the edges of where the gasket would sit when laid on the roof.
3) Do the same as step 2 but on the top of the gasket (this is where the bottom of the mount will mate with the top of the gasket)
4) Install the mount on top of the gasket (it'll stick right on to the the butyl)
5) Cake on blue loctite like a MF around every single thread of the mounting bolt
6) Screw in the bolt as they suggest.
7) for shits and giggles, I would lay more butyl around the edges of the bolt you just screwed in just like you did with the OEM spacer to ensure as well as the rubber washer. Anywhere you think water can enter the system, cover up with butyl.

re: #7, keep in mind butyl will be exposed to the air so it'll get dirty. I was thinking if I put butyl on top like that, I'd strategically cut super thin strips of black garbage bag to cleanly mate to the exposed butyl. That'll cover it up and prevent shit from sticking on to it.

Now you have a perfectly sealed system.

Edit1: Some will argue that the gasket is enough, but I ask those people what the ROI is on cheaping out / being lazy with something so simple yet critical? For an extra few bucks and a handful of minutes, you could have a mounting bracket that you'll never have to worry about.

Edit2: If that OEM gasket from the video is rubber, I would buy a sheet of high temp orange/red silicone from amazon and cut one to size. Rubber dries out really fast in super hot and super cold weather. So, your gasket will fail sooner than later.