I had a new pad, so I'm unsure about prepping the old one, but I acid etched mine and used a product from Sherwin Williams called Armor seal. I've had it on there almost two years now and the only places where it has come up is where a piece of steel or heavy tool hit the floor hard enough to chip the concrete. It's easy to clean, chemical resistant, and isn't too slippery when wet. I went with a color called steel grey i think and it's light enough to brighten the shop up. Good lighting makes all the difference in working in there as well. I have 7, 21,000 lumen lights in my 40x60. They were about $100 a piece on amazon but are on sale now.
https://www.amazon.com/gp/product/B0...0?ie=UTF8&th=1
https://www.sherwin-williams.com/pai...floor-coatings