You might not want to hear this but I wouldn't seal it. For one, concrete wants to breath. It's a pourous material. By sealing it, you could end up with blistering and such. Then, next thing you know, you'll be asking 'us' what's wrong w/your painted/sealed floor.
Also, think about it. I think the reason you want to do this is because it looks 'nice'. Yes, it does, but think about this also - You park your cars on it, you don't eat on it, you don't entertain your guests on it, and you don't use it as a 'sitting room' or anything where it's heated and cooled like the rest of the house. In fact, I bet you spent the LEAST amount of time in the garage than you do any other room in the house. And to boot, those shiney floors can get slippery (but you could use a Gritted-Sealer to help prevent that.)
For me, and I speak for me, garage floors will get dirty and oiled-up and have ALL kinds of stuff spilled on them. Heck, it's just a garage floor. If I ate on it, entertained my guests on it, slept on it, or used it like another room in the main house, then I'd look into making into more than it is. Others will differ and that's OK w/me.
My best to ya and hope this helps.
Jay J -Moderator
PS: God Bless America!