I have used waterglass (calcium carbonate IIRC), used to preserve eggs in years gone by. It stopped a leak in a 389 Pontiac V8 that I couldn't find even after completely dismantling the engine. One must drain the block for winter as the waterglass is rendered ineffective by ethylene glycol antifreeze and it will begin leaking again.

1951 3800 1-ton
"Earning its keep from the get-go"
In the DITY Gallery
1962 261 (w/cam, Fenton headers, 2 carbs, MSD ign.), SM420 & Brown-Lipe 6231A 3spd aux. trans, stock axles & brakes. Owned since 1971.