My 2 cents worth.
When you only replace the spray nozzle and do no other work on the injector you are hoping for the best. When a shop rebuilds the injectors the inside precision surfaces of the injector are lapped on a lapping plate (with 500 or 600 grit compound) to make them flat again. Glass seems to work OK as a substitute for a lapping plate if you do not have one. Regular Valve Grinding Compound is too coarse. You should see a good even gray surface over the lapped area. Clean compressed air is very valuable in blowing out the injector parts to get all the fine stuff out. Dipping the parts in diesel fuel before assembly helps get rid of any lint or fine dust that settled on the parts. If a good job was done lapping the surfaces the proper torque will seal the injector. Also inspect the injector nuts before assembly for hairline cracks or errosion between the spray nozzle and the nut.

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84 300D, 82 Volvo 244Gl Diesel