I think the trick is to read the product descriptions, and see if anyone on Outdoorking or elsewhere has experience with them wassie. The only replacement fuel line and grommet I have personally used was bought from a mower shop, and I have no idea where the shop bought it from. However it seems likely that the shop obtained it from one of the Chinese sources used by a multitude of ebay sellers, since nobody suggested it was a genuine part. Incidentally I only kept that chainsaw for a couple of years, but the grommet was an excellent fit and completely leak free.
The artificial rubber products used for grommets are generally resistant to fuel, and should last for a number of years. What that number is, of course, can only be determined by trial and error. I'm currently playing with a 30 year old Echo SRM200 DA trimmer/brushcutter which still has its original grommet, and it looks good but may have grown slightly since its flanges, while admirably flat, are not really tight on the tank top at this stage. The fuel hose is also original, and the submerged parts of it have grown somewhat, though it still seems to hold the submerged filter successfully. However I am not going to assert that randomly selected Chinese suppliers are using the same synthetic rubber as Echo used long ago. There is a good chance that the available materials have improved, of course, and there may now be cheap materials that outperform ancient premium materials.
