I just replaced both of these seals on my 1520 at 3650 hours for the second time. First time was well under 1000 hours. The seal is a multi-piece seal/sleeve assembly so the pitting on the knuckle casting is not a problem. OP's photos show part of the seal still on the knuckle casting. I recall that when I picked up the seals for the first replacement (25 yrs ago), my dealer told me that I would also want to replace the bearings, AND also told me that best way to make the seals (& bearings) last longer is to replace the front axle oil with 75W-90 or 80W-90 and to change annually (I had been, and still do change annually). The reason for this is that the bevel gears in the steering knuckles are not precision ground gears and as a result they are constantly wearing and creating the metallic particles that you see in the oil. The thicker oil reduces the gear wear as compared the thinner hydraulic transmission oil that is specified by NH, and annual oil changes flush out the metallic particles. The metallic particles which besides causing the seals to wear, also cause the bearings to wear as seen on the tapered roller bearing race in the OP’s photo #4. The remaining bearings in the knuckle are all ball bearings and close inspection will show the same wear as seen on the tapered bearing race. Each time I replaced the seals, I did replace all bearings and also the wheel seals. I have been using 75W-90 since the first seal change and got nearly 3000 hours before one side started to show oil seepage. The 75W-90 oil always looks cleaner, i.e. less metallic particles, at each change as compared to the thinner hydraulic oil did. I continue to use 75W-90 in both of my tractors. The ball bearings are all standard sizes so replacements can be found for considerably less cost than buying through NH.