A mechanic at a Ford dealership quietly handed me 4 flange bolts. 12 point heads. RA offers a Dorman set of 4 for $10. These are at the rearward end of the rear driveshaft.
He suggested to get "the special teflon grease". Will do if it's the only one which'll work. Would Motul Tech Grease 300 do? "High performance multi-purpose grease. Extreme Pressure. Complex Lithium. TECHNOSYNTHESE"
GM has always been the best for me. When I was in college, they would run diagnostics for free on my car, and sold me parts at dealer cost + 10%. I turned around and bought a new Z06 from that dealer when I graduated.