I have an intermittent brake problem with my 86 corvette , twice the peddel went all the way to the floor on my wife. after she pumped them they came back. Brake fluid is full
Brake master cylinder is bad.
You may have air in the lines. Have a "good" reliable break shop check it out and perhaps a full proper bleed will fix it. I just replaced the 47 year old master cylinder on my Vette when we had the engine partially disassembled, only because we were working around it and I had the money and time. Made no difference except the peddle takes one inch further to engage. I have to re-bleed the system because when I step on the break peddle I hit the throttle. If there is air in the system, it will act like what you describe. Better to have a break pro look at it instead of an insurance adjuster.
Search Chevrolet Corvette Questions
Are you a UK consumer? CarGurus now has a discussion forum in the UK.
Chevrolet Corvette Experts