I use Viton- a flourocarbon rubber- for everything around my house and shop, including garden hoses. It is proof against anything liquid in a car. Stay far away from butyl or neoprene rubber which are undependable even with plain water. McMasters-Carr has o-rings- NOT made in China-, and if you run into an oddball size, it's possible to make your own! There are build-your-own o-ring kits available. In the outer space biz, NASA contractors routinely use bulk o-ring stock with the ends carefully super-glued together to create gigantic o-rings for sealing 10+ ft OD segmented booster rockets. This works best for non-moving o-rings but if the motion is slow, it also works on other types. I once fixed a badly designed Camaro master cylinder with a second o-ring seal for backup on a modified moving piston, and my glued o-ring held pressure for decades. There's a POCA newsletter article way back in the web archives on this, with photos.