if there is no present apparent leaking of oil in and around this duct taped area, then it is hard to say without removing the tape why it was ever put on in the first place, unless of course it was to stop any pin hole leaks.(corroded copper tubing)
The one thing about furnace oil is IF there is a very small leak it will show up in and around this taped area.
the old saying of ..."if it 's not broke, don't fix it, applies here.
I do not know how handy you are, but, if it was me , I would have the necessary repair parts (flare coupling, copper tubing,) and tools(flaring tool, tube cutter,) on hand, just in case.
I would first shut off the POWER to the furnace,then close the oil VALVE at the tank. I then would remove the tape and inspect the line to see if it really does need replacing.Hopefully, there is no leakage and why the tape was ever put on we will never know.
But if it does leak,I would cut it back a foot or so from the leak and remove this section right back to the filter.(make sure you have an empty container to catch any oil) Using a new coupling and existing filter connecter, I would flare and re-install this new section. Open oil valve, check for leaks, then turn the power to the furnace back on.