Universal o-ring sets are available all over the place. They can be had in neoprene, viton, silicone and just about any other material you might want. I have several sets but my go-to is a couple of drawers in my parts bin that have small and large o-rings in them.Since this is such an active thread does anybody know the part number for the O-ring that goes on this coolant tube into the block
I have collected these from many sources. Every time I do a head set on an injected engine it comes with a set of o-rings for the injectors but usually the injectors don't have to come out so I wind up with dozens of these. Many gasket sets come with extra o-rings that are intended for another application or for something I didn't take apart this time. Water pumps, fuel system parts and many other parts come with extra gaskets and o-rings. I save them all and I rarely have to buy an individual o-ring any more.
Some people get all upset if the o-ring isn't exactly like the one that came out. I have found that if it fits the id and od of the parts involved or if it is in a groove and stands proud of the groove then it will seal.