Check the area where the Cone shaped part of the Hard Line seats on the Injector itself for cracks or marks going acrossed the seating area.
If any dirt gets between the Hard Line cone and the seating area on the Injector it will leak. If there was dirt their previously you will see pits where the dirt was squashed into the Metal (the metal of the Injectors is softer than the metal on the Hard line cone).

If you really need to get the car on the road I have more than twice (where I used to work) used a small thin Copper Crush Washer put into the Injector end between the Cone and the Injector. However, you need several crush washers as it does not always want to center on the first try.
Where I worked we had a 1 foot squre box of misc Copper Crush washers and O-rings left over from gaskets kits for rebuilding Fuel Injection Pumps so I do not know where you would buy some tiny Copper Crush washers.

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84 300D, 82 Volvo 244Gl Diesel