I find repacking wheel bearings pleasurable and zenlike. Never had to replace one I packed. I used to clean them with a solvent and let air dry first to make sure there wasn’t any dirt in the old grease. I think hand packing does a better job than a bearing packer.
@ok4450 - just wondering, what indicates that the bearing has to be cut off? I haven’t worked on these in years, I’d like to know the signs.
I’m pretty sure that it is not the front wheels of a 2wd Pathfinder. They would not have the splines on the outside like that. That also pretty much rules out tapered roller bearings. The only reason I can see for tightening the bearings would be if it has captive rotors that had to be replaced, other than that, there is no reason to remove the hub.
The picture looks like it spun the bearings somehow which would mean the axle has to be replaced, but the wheel is not going to fall off. It could be an optical illusion due to the discoloration though. Anyway, I have not seen a reason to have removed the hub in the first place.
Someone must have replaced the rotors or repacked the wheel bearings. The maintenance schedule indicates to repack the wheel bearings every 30,000 miles.
I’m impressed that Nissan uses serviceable tapered roller bearings on the front hubs.
My reason for thinking on the cutting comment is that the slot could be the result of a die grinder.
The end of the slot looks to have a little purple in it which I assumed to be heat due to a die grinder wheel.
The debris on the threads looked like metal particles from grinding.
Then again, my close range eyesight may be not be that great (I don’t wear glasses except at gunpoint…) and I could be dead wrong about all of it. 
The slot is for a locking tab that fixes the lock washer which fixes the spindle nut.
My 4WD 1970’s Ford truck uses tapered roller bearings on the front wheels that require manual repacking from time to time as part of the truck’s routine maintenance. It’s fairly easy to do so I do it as a DIY job. The bearing surfaces have never looked scored like that in 40 years and over 250K use. There’s some signs of wear, but it is uniform wear over the whole surface.
All that said, I doubt this problem will cause the “wheel to fall off”. It may start to create some wheel bearing noise at some point though. With 200K on the vehicle, probably the best strategy is to monitor the wear patterns over time.
The axle is not the part to replace. That is the Knuckle that has the wear on it.
From the photo I would think that you should replace the knuckles and bearings.
I presume just the front is affected.
But without having the thing right here to feel weather those are grooves or just discoloration…hard to say.
Yosemite
Thanks for all the comments - I’ve noticed no noise at all and the Pathfinder drives fine. It sounds like the consensus is that a) the wheel isn’t likely to fall off and b) I should get the bearings redone by a quality shop.
It’s the front axle.
I think you should find a good independent shop and have them replace the bearings on the front. Show them the pictures and ask them to give you a third opinion on this. With them having it “In hand” they may just say the knuckles are fine.
Either way, with the number of miles on this car…it could use a set of bearings.
Because I do my own, I’d just wait for them to start making a little noise.
Yosemite
First, my bad, but we have all been fooled by the pictures. The drawing supplied is not real clear either so I looked this up in the FSM for my 97 Nissan PU. The 4wd uses the same system but the additional drawing tell a different story.
The grooves that the dealer said were dangerous are not. That is total BS by the dealer as these are cast into the axle, and that is the axle that is shown, not the spindle or the steering knuckle. The machined surface between them is where a needle bearing rides. The needle bearing goes between the steering knuckle and the axle shaft. The spindle of the steering knuckle is not shown and that is where the inner race of the wheel bearings ride on. The spindle of the steering knuckle is hollow for the axle to go through.
Since there is no picture of the steering knuckle, I cannot judge its suitability for reuse, but I doubt it has any problems or surely the dealer would have tried to sell the OP new ones. You do have to remove the hub in order to get the rotor off so that does expose the wheel bearings. The correct procedure for tightening the wheel bearings is a lot more complex than for typical front wheel bearings on a RWD. Its got like 5 steps, not the typical two that we are used to.
I agree, go ahead and get new bearings. I would while everything is apart. But I do not think that the Firestone place did any damage, that is just more dealer BS. I would also recommend that next time, find a good local independent to do maintenance on your vehicle.
The idem in the picture on the left is a steering knuckle/spindle. The tip of the axle is visible at the right edge of the picture. The picture on the right is the inside of the hub.
I didn’t see any mention of groves, a picture of the under side might show wear.
The discolored/dark areas are evidence of heat exposure but I don’t think the is a risk of the spindle breaking.
That is not the steering knuckle, it is the backing plate where the axle comes through and the axle itself. The discolored areas are not heat scorch, it is as cast finish.
Edit: I went back and blew up the picture a little and now I stand corrected, it is the steering knuckle. Your eyes are better than mine, going to visit the optometrist soon I guess. They are scorch marks and they appear to have some wear which would indicate a spun bearing. I’d suggest that they be mic’d to determine if they can be reused, its hard to tell from a picture.
I guess I owe the dealer an apology too.
You had me scratching my head for a while @keith. I got out my best $4.99 reading glasses and looked. I sure was glad that you posted the correction. I wish that the OP had wiped all the grease off the pieces and layed them out on a clean towel to photograph them. But all is well now… Maybe.