The injector nozzle's body is in two parts that screw together. There
can be a small leak - oozing - at the seam and that's, I believe the
cause of your engine's leak.

You can fix this. Slightly loosen the high pressure pipe to the
injector. Use a large waterpump plier to tighten the injector's top half
to its bottom half. Yes, the injector is torqued into the cylinder head
by 50 ft lbs - that's not being disturbed, you're only tightening the
top half to the bottom half. Don't expect much movement from your effort
the top will probably only move a couple of mm at most.

Carefully tighten the high pressure line to the injector JUST SNUG, NO
MORE. These are pipe compression fittings and over tightening them will
crush the pipe and it will leak until you replace it so be cautious and
rather tighten it a couple of times, until it no longer leaks. I believe
the spec is only 15 ft lbs.

As to your question. Newer Bosch remanufactured nozzles have a finer
spray pattern than the original nozzles. The opening pressure of a new
or remanufactured nozzle is higher than old nozzles so they really
shouldn't be mixed. I replaced all five, in part for that reason and in
part to have a cleaner burning engine. But subsequent single
replacements were made to no ill effect.

Diesel injector repair shops are often found near larger cities and such
shops can rebuild and calibrate your injectors - check the local phone book.