I think that's a head bolt washer you are seeing.
Eddie

I agree

yes,its to high to be a freeze plug.

Yes, that's a head bolt.

could a small amount of reversion,be causing this???

Possible, but it is on all 4 sides. And wouldn't it be salt then? I'm still thinking some sort of fuel additive.

Do a bleed down test, my bet is reversion and leaky valves. I have seen this on several 525's with high bleed down numbers, some over 50% with less than 150 hours on them.

I finished breaking down the engine. There was some salt residue on the exhaust runners. Maybe it is reversion an just something in the water.

PSI check your headers if you haven't done so to rule that out.

Have not done yet, but I am now in the tiresome habit of pulling and testing them every winter, even with the new Hardins. So far they have been good, just one pin hole.