N14 front main still leaks after replacement

Have you checked for end play on the crank?

 

Correct dipstick?

 

Sorry I can't help w/ N14 specifically... but you say everything else is good.
If so, a new harmonic balancer
A sleeve if one exists for the balancer?
Your Main bearings are too sloopy.

 

Does it leak from where it contacts the crank or around the circumference of the seal? All I can suggest is measure the run-out of the crank with a dial gauge. Usually leaking seals means incorrect installation, but I guess you must be doing all that OK. Pre-lubing the seal etc.
What do Cummins and the seal manufacturer say?

 

I do not know what you are missing and will answer this question as crankshaft seals in general. Some of these I am sure don't fit but I will just through everything I can thank of in the basket and hope pick out one the helps you.
N14 cannot leak oil past the bolt threads because there is no sealant on them?
Leaks oil between the balancer hub and crankshaft.
Cummings seals are to be installed dry.
Had a problem with an after market seal. Thought it looked funny anyway but installed it. Installed factory seal from Cat, it was a Cat, no problem.
Crack in the balancer at the key way. They can be really hard to see.
Have seen problems with seals ####ing at the beginning even with the proper tools. Watch for that and hand tools only.
On sleeves and seals like that I have been using anerobic sealer for years. That red stuff they glue Detroits together with. Dries only in the absents of air. I feel it lubricates the seals and sleeves for easier installation. Seals any imperfections such as lines in housings from improper seal removal or spaces under wear rings.
Does it not actually run on the crank nothing to do with the balancer? Install the seal 3/16 of an inch farther so it is on some new meat.