On 21 year-old paint, I hate to tell you, but it might be going down...
Not knowing anything about how the vehicle lived during those 21 years, ( Inside when not driven, etc., outside 24/7, full sun, etc...) if it was in my shop and I measured the total thickness, and it was at a high level, I would experiment carefully, with a really fine polish on a little spot hopefully somewhere where it would not be too noticeable, and see if the fine polish could remove the cloudiness...
I had a new Chevrolet Truck in Metallic Blue, in one of those years back then, and the entire paint went bad fairly quick and they had to take it back and repaint it....
Good luck with this....