GM 12-Bolt Advice Needed

My bracket race car is a 71 Monte Carlo 408 BBC with T-400 & 12-Bolt Rear. Eaton Posi unit, with Richmond 4.10 gears. Heavy Car, (3750# without driver), fairly mild combo. (12.30 @ 108, 1.71 60').
Problem: Broke a Spider Gear (pinion Gear) last season, which trashed pretty much all internal differential parts. Replaced posi with identical unit, which was in very good condition. New R&P gears, bearings, etc.
10 races later, (72 passes), I was pulling routine maintenance, and Cross-shaft in Posi unit is severely galled, as are the spiders that ride on it. Had been using synthetic 75W90 oil for years, when I repaired it last year, Richmond suggested petroleum-based 85W140 instead. The cross-pin is very poorly lubricated, but this is incredible how bad it got chewed up, and how quickly! Okay, 3 questions:
1. What caused this rapid failure? Cross-shaft was "Yukon" brand - could be Chinese sh!t metal?? Or weak clutches in posi, causing single-spin?
2. I cannot get the cross-pin out, I beat on it for almost 2 hours, and it is halfway out of the housing. So I cannot remove the axles, or the carrier. Do I need a cutting torch to get this shaft out? Or?? Anyone had similar experience?
3. Pretty-much decided to go to a spool. I have some GM axles with C-Clip Eliminators on them. But no installation instructions. I am told I have to cut the ends off my axle-tubes? Anyone done this before, or have some instructions on what I need to do to use these? Looks like the bearing retainers are split in 2 halves, do I sandwich the backing-plate flange between the 2 bearing blocks?
Thanks in advance for your help.
-Jim.

Tell you a rear-end story from my own experience as a Chevy guy for decades.

The 12-bolt is MARGINAL for the abuse of drag racing. An acquaintance was going through two or three per season in his 4-speed, wheel-standing Pro Stock '70 Camaro.

He switched to a Ford 9-inch, which would go for a whole season, but no further.

He finally settled on the Mopar 8 3/4. It has bigger bearings than any other passenger-car unit. One of the reasons Chrysler almost went broke in the early '80's was they put this SAME studly pumpkin in everything from Slant 6 Valiants to 440 Roadrunners; only difference was axle length. (Hemis often got Dana 60 truck set-ups)

After 150,000 miles behind a 6 or 273 2-barrel, these rear ends are like NEW and CHEAP in the junkyard. After a pro rebuild they are half the cost of a 12-bolt or 9-inch.

My friend's race car gets 2-3 YEARS from these "secret weapons", and one of them is bulletproof in my son's 400+ hp '63 Chevy II 100 post.

Your spider gear/cross shaft problem are one and the same. Your posi unit is not working all that well. When one wheel spins significantly faster than the other, the differential spins around very quickly. This slings all the oil out of it, and this is while the spider gears are spinning like mad. you need a better posi unit. Since you are running a drag car, put in a nodular unit. They are noisy when turning, but how many turns do you take in a drag car, right? I see this problem during the winter in both FWD and RWD cars and trucks during the winter. People just love to spin the wheels on ice, then BANG, the diff lets go and they need a tow. Very often the diff pin exits the rear cover, or the FWD trans case. Good luck, Also make sure you are running the correct lubricant for Posi diffs.