It depends on what is causing the leak.
If the Hard Fuel Injection Line is leaking due to a pin hole or crack Tightening it in the end will not help. The only fix is to replace the hard line.
Another issue can be that the Cone shaped end of the Hard Fuel Injection Line can get a dent in it from previous overtightenings that has dameged the sealing area. Again the Hard Line would have to be replaced.
A similar thing can happen to the funnel shaped threaded end that the Cone fits into. Again you would need to replace the upper 1/2 of the Injector Body (you have to loosen it and do a visual inspection of the end, right above the cone is also where the lines like to crack). If you Change the upper Injector Body the Injector will need to be Pop Tested as changing the body will change the tension on the pressure spring inside.

There is something that does not happe often but the 2 little nipples that the Fuel return hoses slide over sometimes leak were they are attached to the Injector Body.
They are press fit in and they use a circular tool to swedge/deform the metal over them. Over time they sometimes get loose enought to leak. There is no way to fix that.

May be there is a member close buy with an extra used Injector that you could swap to see if the leaking stops. At least that would tell you if it is the Injector or the Hard Line.

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84 300D, 82 Volvo 244Gl Diesel