Go to Home depot and buy a big crayon of 100
5 silicon sealer and a gun to put in in. Turn your waders inside out and dry them and then take rubbing alcohol and a rag and give them a good scrubbing and let them get bone dry.
Thn squirt that stuff on liberally, especially on the seams.
I tried that spray on flex seal stuff thinking it'd save the day, it was a failure.
If you are really in a pinch, you might try wearing a lightweight pair of dryfit waders on underneath the leaking ones. I've done that and it was a success.