Time to contact the supplier of the new units. Hopefully the fluid was flushed before the new calipers were installed. Brake fluids, and especially heat temp type fluids seem to have an affinity for moisture, this is most often a problem.
Old brake fluid and Chevrolets four piston calipers with long periods of sitting is a common problem. There used to be a kit to resleave the calipers for these.
I remember the bus driver we had when I was a Freshman and a Sophomore in High School. #1 we weren't a bunch of smart asses anyway. #2 He had a radio on the then popular WIND, "The windy city station" that played the top forty type of music and he had added a couple of speakers along the top of the windows inside the bus. Everyone was just sort of bobbing and weaving in their seats and we never ever had any sort of discipline problems. The old say "Music soothes the evil beast" seemed to apply.
I would read the instructions. The instructions say to wait 72 hours before applying the varnish. While the first coat of silver looks great and I didn't have any issues with minimal handling I think that in the long run it would be best to use the varnish as they suggest protecting the finish in the long run. I didn't notice any changes in the finish after the varnish had dried.
I can see why you wanted to build a model of the real car. Beautiful paint finish and like the clean understated look of the body without a spoiler or stripes. The yellow color optional custom interior really stands out and not often seen even with a black car. Great looking engine detailing and the dish slot Ansen style wheels were popular when this car was new.