Thanks for the info. Unfortunately, the closest hobbytown USA from me is like an hour drive away. They do have flat rate $4.99 shipping, but I still would have no idea what size to get. I only got the Danco #60 because the person who made the video said so. I've been satisfied with the fix on the iStick more than the MVP.
The MVP didn't sit exactly flush. The iStick is close enough, and I didn't take out the old o-ring either. I'm just happy at this point that I can grab any tank from my drawer, put it on the iStick, and it will always fire.
This is for my own records. It looks like the Danco ring is 6.35mm wide (outer) x 1.58mm thick. So you would have to get something thinner than 1.58mm to help make it flush. The hobbyworks web site doesn't have a lot of details on the dimensions of a lot of the o-rings. I'll just keep this in mind in the future. Like I said, my iStick works fine right now, and this should take care of me at least until the iStick 2 comes out sometime.
While I was looking, I found something that may work. It was on the hobbyworks web site, and they sell the same one on amazon for $4.48 as an add-on item, or $4.48 on ebay. It's 5mm (inner) x 1mm (thick). The outer diameter is 6.5mm.
The model is Axial AXA1162. Still might not be thin enough, but it's another option I guess. I'm not sure if I would waste my time redoing it with this one. I wouldn't want to end up breaking my iStick trying to take that other one off. Not sure how much 0.6mm in thickness would matter.
Amazon.com: Axial AXA1162 O-Ring (10-Piece), 5x1mm: Toys & Games
New Axial O Ring 5x1mm 10 AXA1162 | eBay