You can re use the old plug, if its a metal plug. Be warned there were some rubber cap type plugs made for this purpose, but they tend to blow off so don't ever use (or re-use) them. Only use the metal piece with barbs that dig into the hose like the barbs on the injectors. You can cut the old hose very carefully using a sharp knife. I've used a some sharp dikes (diagonal cutters) successfully too.

The plug on #5 on my 300TD blew in the middle of the desert once. It is amazing how much fuels squirts out of that little spigot!
I was leaking fuel so bad that I was misting cars behind me (one fellow who tailgated me a short while switched on his w/s wipers and hit the wash button and he suddenly dropped back about ten car lengths, I think it messed up his view pretty bad (good way to get rid of tailgaters huh?) anyhow I finally found a gas station and stopped to try and fix it becaue I didn't want to find the car ablaze with fuel dripping down on the exhaust line!

Since the plug (and line) was long gone I found that I could cut off a short hunk of the excess line that runs from the filter housing to the #1 injector and found a machine screw and used it as a plug and that worked well until I made it back some 150-200 miles.

I am now testing Viton hose as return lines on a 603 engine. So far it is holding up very well. I will post results about a year from now as to their longevity. I believe Viton will significantly outlast the OE hose material. The reason the material deteriorates so fast (18 months is about all it is good for) is because the fuel is really hot coming off the injectors and hot fuel aggressively attacks the OE rubber and it gets soft and fuel weeps thru.

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'95 E320 Wagon my favorite road car. '99 E300D wolf in sheeps body, '87 300D Sportline suspension, '79 300TD w/ 617.952 engine at 367,750 and counting!