Whats best to replace rubber oil/emmisions lines?

Bo, what year and model are you working on? There are many options of materials available. First you need to ask yourself whether you want an original look on the installation. If that is important to you your options are fewer. If not I would use a hose made of Viton "Trade Name" or material classification fluoroelastomers (chemical name: fluorocarbon FKM). Your parts counter guy is correct, the fuel line he is most likely talking about is Viton. In hoses it is mostly colored black, but in other forms it is colored green. Green like o-rings for air conditioning refrigerants. Next you will need to now the size and what wall thickness will fit in your installation. I would assume you need metric sized flex hose so don't settle for something oversized or undersized. Compromising size for an installation is asking for problems or makes it hard to install. These are oil return lines so the pressure is very low. There can't be more than 1 atmosphere inside the engine so plan for 14.7 psig which is standard range for fuel systems using carburetors back in the day when carburetors were king. Newer fuel injection systems are upward to 100 psig and will be stiffer and thicker walled hose which makes it harder to install and your hose clamps may not fit.

 

The oil return hoses were never cloth covered. BB or TR, they were always plain black rubber.

 

Yes, if it's good for fuel, it's no problem with oil. Both hydrocarbons, fuel is just more volatile and more aggressive than oil.