Hello,

My fuel lines rusted and developed a leak.  I found a Dorman replacement for the Supply, but none for the return line.  Also, at the Fuel Module Connections for these lines, there are some very small O-rings on the Module end fittings which I want replace.  Does anyone have experience with replacing these fuel lines and know a source for these O-rings and a new return line?  
Thanks

You can most likely stop by harbor freight for a o-ring kit. They have good assortment of sizes. I'm going to assume without seeing the connector it's like a A/C lines you'll use a release tool to push the locking spring back to release the lines. I typically got a lot of o-rings from A/C kits. They work good in power steering and fuel systems.

Mike, thanks I do have an assortment of AC green O-Rings, I was unsure if they were suitable for gasoline. 

Should work out fine. Just assembly and get it fired up and watch for leaks being if rings are too loose might weep or to big it might nick the o-ring on assembly. Might also be good to spray the connector and o-rings with silicone spray makes assembly super easy and less likely of leaking.

C2500 with a 4.3  thought all 3/4 tons had V8

Have you looked at rockauto for line kits or new modules, should come with everything you need.

Help section at part stores carry fittings that snap on modules then you can use rubber lines.