Water Leaking into Subpanel from Upstairs Laundry

We have a subpanel in our basement that happens to be underneath our upstairs laundry room, as we found out today. Something funky happened with our washer, and we had water leak out. It ran down the wall, down the romex cables, and into the subpanel. How would you recommend sealing the top where the romex enters the panel? Note: this box is between studs behind sheetrock.