The '86-'93 rear was about the only bumper saved complete for some reason, all the marginal covers got chucked & aluminum recycled.
Shoot a message if you wish.
The 1973+ alum bumpers fall off the salt air/coastal cars/salted air+ salted road New England cars.
Most of the poor sods on the east coast have to get pretty creative...
-Larger holes/stepped studs
-Sacrificial zync paste
-wood instead of metal? (seen it

).
-Stainless with appropriate paste?
-Under car deflector/actually preventing the spray from ending up there from both running down the tail gate and spraying up from under the car and being caught by the bumper like a big sail/umbrella.
Absent something to direct the spray from under the car the studs galvanically corrode the extruded alloy they're pressed into...just a big nasty condensation/salt air trap back there.
Even the V70s/super seam sealed/well galvanized 1991-1993 cars have corrosion/rust issues back there on the 240s in New England fog+ salted road brutality...the salt water literally just sits right on top of those studs and increases in salinity/never dries completely until it gets hot enough for the alloy to disappear around the nice hot stud pressed into it.
You couldn't design a better galvanic corrosion science experiment short of maybe adding electricity/ precisely temp / pressure controlling above & beyond existing environmental conditions?
See what you mean about the cover, 2manyturbos...similar, but different.
The aluminum extrusion for USA/CDN '86+ & shocks are vastly different in strength & construction/basic appearance from '83-'85.