40 flat six Pontiac coolant leak exhaust guide

[40flatee]

I have a 40 Pontiac deluxe with the flat six that I found coolant weeping out of the #3 exhaust port when I removed the exhaust manifold. This particular exhaust valve gave me trouble last year when it stuck. I removed the exhaust valve, washed the guide with brake clean and lubed, and installed a new valve. I now believe it was sticking due to corrosion from water in that port. Do the guides pass through a coolant jacket? Do I need to consider a cracked block from the guide corroding and swelling? If so, can the block be repaired?

[Oldtech]

The guide itself isn't exposed to coolant so possibly there is a crack somewhere. Most likely place in my mind would be around the valve seat somewhere. It it were me... I would put 1/2 a bottle of irontite in the radiator and drive it.  Works for me on tractors.