I am told this is a very common issue with the aluminium bumper box bolted to the steel bumper shock plates (not sure if I got the actual part names correct, but hopefully you get the idea). I have had to resort to using ratchet straps to hold the bumper in place until I can find a way to fix the issue. Has anyone advice as to the best way to repair this? I am told that even if I could find another aluminium box, I wouldn't want to put it on as it will give me the same problems down the road. What fixes have been tried? (My chrome bumper is perfectly solid and still has gleaming chrome).

 

Unfortunately, your info is correct. Not sure I'd call it "common" but definitely it happens. The phenomena is called galvanic corrosion, which happens when dissimilar metals (like aluminum and steel) come into contact with moisture (especially salt slush). The design of the aluminum reinforcement makes it worse by trapping that salt slush inside the channel. I took one apart a while ago and while not falling off, it was definitely badly corroded. Short of finding a good replacement aluminum reinforcement, you can patch the old one with aluminum plate and a TIG welder. Use a plastic spacer between the aluminum and steel to prevent direct contact between the two.

 

As Joe said great idea. I do recall working in Olds dealership body shop the factory used fiber shims between the 2 on some models

 

I recall during the period when these vehicles were daily transportation, many upstate NY Cutlass's with a pressure treated 4 X 4 for the rear bumper.

 

My '81 Regency bumper fell off onto the road when I ran over a small bump.

 

There must be some donor cars that could be used to help your ride.
I looked at DVAP and found these offerings that appear to have excellent potential for both bumper and bumper supports. I believe that any Ninety Eight or Delta 88 from 1980-1984 (Delta to 1985) will have the right parts you need. Good Luck, I hope you find what you need. One good thing about the storage location of DVAP is they don't get much rain there so the cars are likely non rusty. I remember both of my 1983 Ninety Eights and they are really nice riding cars.

1985 Delta 88

https://www.dvap.com/salvage/1984-ol...dan-840l6060c/

https://www.dvap.com/salvage/1983-ol...oor-83ol2988d/

https://www.dvap.com/salvage/1983-ol...dan-830l2171b/

https://www.dvap.com/salvage/1983-ol...dan-830l8579d/

https://www.dvap.com/project_car/198...-98-83ol2988e/

https://www.dvap.com/salvage/1983-oldsmobile-delta-88-royal-2-door-sedan-830l8579d/

https://www.dvap.com/salvage/1980-oldsmobile-98-80ol2947c/

 

Yep lots of GM cars had wooden rear bumpers as early as 1980, around here. The weirdest bumper issue I remember was on a full size 1976 Ford wagon. I had it jacked way up and went to step on the front bumper to reach under hood, and it fell off on the floor! Can you imagine if that happened while driving down the road and running over your front bumper? They were huge bumpers!