Bob, I would suggest you do what Dwightparks does. Get at least one replacement cap and seal along with a bottle with enough oil to fill one hub. Keep it in the truck or boat. I have seen cases where those caps can get hit and cracked or broken.
I was told they would go 100,000 miles easy. Not sure I buy that. I keep spare o-rings and outer cap that has window to see oil level and condition of oil. I change oil about every other season. Using 50 weight valovine racing oil with no issues.
Bob, I would suggest you do what Dwightparks does. Get at least one replacement cap and seal along with a bottle with enough oil to fill one hub. Keep it in the truck or boat. I have seen cases where those caps can get hit and cracked or broken.
Proud Member of Team Geezer
Charlie Weaver USN/ENC 1965-1979
I still have the old grease jurk kind. lol Grease them up every year, still good.