Did it get on the carpet? Can you access the core from the cabin? I had a core leak and I put baking soda on the carpet and let it soak it up then vacuumed it up and repeated until it was gone. If it is in the core housing and you can access it then squirt solvent and soak it up with a rag. I don’t understand the number of cores that are being replaced. The system must be over pressurizing and blowing out the cheap cores. Has the radiator cap been replaced?