Rear differential issues

I purchased a 08 crew cab max 5.7 li
4wd vin # 5TFDV541X8X037871, about a year ago.

The truck was in great shape and has been dependable. I had a mechanic look over it and drive it before purchase and he gave the truck a 9 out of 10.

The undercarriage had been sprayed prior to my purchase which was a bonus being that it was from the south and had not seen a Mn winter. Unfortunately the idiots that sprayed the carriage also sprayed the relief valve which in turn caused the seal to leak. About 6 months in I noticed fluid on the driveway coming from the rear diff pinion seal.Brought it back to the same mechanic and he didn't want to work on it (hes 79 yrs old). I'm pretty good with tools, so I watched a YouTube video and started in. My first attempt I was unable to move or budge the pinion nut, and fishing season had started so I kept an I on the fluid level and temps and made her through season. I fish about 200 days per year. My plan was to get it fixed over winter. After multiple attempts with impact of diff size, cheater bars on manual breaker bar,I simply couldn't get that nut too budge - and yes it was unstaked.
I did not try heat but that was suggested, I'm a pipefitter by trade and know what heat can do to metal if you don't know what your doing, and was trying to keep this repair as simple as I could being I had no other symptoms than a small leak. At wits end with frustration I decided to remove it using multi tool, Dremel, and drill bits. Took a bit of work but I removed the nut without damaging the threads of the pinion. Unfortunately there is a groove in the companion flange wear the seal seats so Id like to use a sleeve but can't determine whether it's 9.5 or 10.5 and worse had no intentions of fuckin with gear ratios and preload. Best I can understand is
the crush sleeve is already at specified torque so plan is to
- get repair sleeve once identified size?
- hand tighten new nut to where old nut was by counting turns
Should I add something like loctite as well as stake it?
Once this is accomplished I'll keep a temp gun to monitor for over heating of diff and listen for obvious sounds. and cross my fucn fingers cause this is all or none as far as i go. Any help on size of sleeve or how to determine it is appreciated as well as any other constructive advice towards putting things back together.

 

5.7 has 10.5 rear axle. It uses a solid sleeve, not a crush sleeve, no need to worry about preload. Replace the flange and seal, torque pinion nut to 224 ft lbs., stake nut. I never re-use the nut, or use loctite, but probably be fine.

 

Thanks fellas I've spent countless hours researching what I got myself into that included many hours on this forum amongst others, but putting it all together for gear type, preload, etc. . I really appreciate the your time an knowledge! Ill update once finished and feel confident things are going to go pretty damn good.
I'm a journeyman pipefitter/plumber if you are ever in need of anything pertaining to those areas do t hesitate ask.
Cheers