Your engine had virtually no cooling. All channels in the seal are overgrown.
In my opinion, these problems arise from the use of coolants that are not compatible with aluminum. Or driving on water 
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While I have an active thread going. It’s clear that my cooling system needs attention beyond just the replacing of tough to reach hoses. I’m going to endoscope the radiator to check it and at least give it a through flushing. - and replace the water pump while I’m at it…
Any opinions on sourcing the 4.0 water pump? Rebuilt original at $200ish (jagbits) or a aftermarket for $60-90 (rockauto)?
a week ago I exchanged for a good quality Chinese replacement with →
https://www.sngbarratt.com/English/#/UK/parts/c157de11-4c8c-4225-bb78-facc8d32d3e9?fromList=Search%20for%20`EBC8550`
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That is going to be VERY challenging to repair properly: unattended, it will not work.
Well, now you’ve done it. Challenged me…
“I’ll show you!” 
Not me you’re showing: it’s physics.
I seriously doubt anything short of welding and remachining is going to fix either erosion.
I’m a huge proponent of J-B Weld…but not here.
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Duly noted. I’ve resolved to take all evidence to the machine shop for a proper second opinion, but sincerely thank you all for your insights and opinions.
I genuinely appreciate everyone’s time on this forum. As a serial wrencher and hobbyist I am a member of quite a few forums, and this one is certainly one of the most knowledgeable and generous.
I’ll keep the thread updated as I know more.
JitneyBead
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I agree. J-B may patch some of that corrosion damage, and for some amount of time. But not permanently.
Hardfacing → risk of block stress and subsequent cracks
Grinding → possible with 1mm and a thicker gasket should be used, not possible with deeper pits> 1mm
In my opinion, the block to be replaced