You most likely need a torch to get the spindle off. I always do, even though I put it back together with anti sieze.
For what it's worth, I went all the way in to U-Joints on mine and didn't have to use a torch but that's because I didn't have one at the time. Just an impact gun and a wrench.
I do live in the northwest and don't have to battle vehicle rot from salt. Watching videos from South Main Auto on YouTube, he's up in the northeast and some 10 year old cars I see roll into his shop have more rust than my Explorer. Amazing that the city/state allows that.
I highly recommend replacing the spindle bearings. They're an overlooked maintenance item that can cause a lot of 4x4 noise. NAPA BRG BK1 will fix you up.
Regarding the o-rings, they're a special kind that have flat sides. You can probably get away with a regular o-ring or RTV but I'll help you out. Call up MileMarker and get part number 428-03. They were $10-15 for the set, shipped. That's the original o-rings included with the MileMarker 428 manual locking hubs for the Explorer. I imagine the Warn ones have the o-ring in a very close spot. I can verify if someone gives me an ID or OD of the Warn ones.
Another thing I forgot to say is that with the manual hubs, having the o-rings installed doesn't mean you'll be safe from water. Based on recommendation from this site, I wanted to clean my manual hubs up so I soaked them in ATF. That is, until the ATF trickled out the bottom. There's no sealing on the selection knob end of the hub so if you get that dipped into water, it's going to get into your wheel bearings, no doubt about it. Regular road grime and moisture/rain shouldn't though.