36 -- used Irontite with excellent results. Tried the usual stuff on the shelves - Barrs Leak, Barrs aluminum / copper, they did not seal the leak.
Just get your block super clean, all traces of anti freeze should be gone. I used the Irontite cleaner, ran it for hours. Also used a dishwasher detergent pod, rinsed and back flushed. Mixed the Irontite in a bucket and added it along with water to the cooling system. Ran it for hours. Drained the cooling system. Irontite needs to dry/cure to be fully effective. I removed the thermostat housings (8BA) and lower radiator hoses. Let it sit for about a week. Filled it with bottled water and water wetter (2 bottles). Just follow their directions, and you'll be pleased with the results.