I've never seen an issue with gold.
I didn't change the gold in my truck for almost 10 years and it was immaculate. And all the other fords ive worked on with gold coolant had beatifully clean cooling systems.
Plus the 6.0 head gasket issue was adressed by ford by using better head bolts not changing the recommended coolant.
We never had a problem with the Ford gold coolant, if someone mixed green with it no harm was done except shortening the flush interval. There can be some nasty stuff in municipal water,is that what FIAT chrysler uses for their factory fill? I've never had experience with dex cool, closest thing was the orange coolant used in hybrids.
I hate sellers who try to hide problems from buyers, I replaced the rear rotors and pads before turning my 2011 Ranger over to the new owner last fall because I wanted everything to be 100%. We used to have people trade vehicles with all kinds of hidden problems- one 4x4 didn't have a differential carrier or axles in the front end, for example. If a customer does that he got a good trade allowance, if a dealer did it he's a crook. Nope, they're both crooks, it's just that the dealer has no recourse and the customer can call the BBB or the state's consumer protection agency.
I have experienced it first hand. If you got ten years out of G05 without servicing it, you did well. Even Ford recognized there was an issue with it's use in the turbo diesel engines and put out a document shortening their original coolant lifetime and giving specifics on additives and replacement intervals (I don't have the document and I'm not going to look it up, but it have seen it before). You can go to just about any PowerStroke forum and read all yo want about it. I doubt the G05 would be much of a problem in most engines, but the 6.0's oil cooler has VERY small coolant passages and when the coolant begins to break down, the goo created begins to clog those passages. Eventually, there will be enough blockage to limit the flow to the EGR cooler and this just exacerbates the problem by superheating the lesser amount of coolant flowing through the EGR cooler. If the cooler ruptures, any coolant that finds its way into the exhaust gas part has free flow back into any open exhaust port on the passenger side head. Not to mention, directly into the intake the next time the EGR valve opens.
To my knowledge, Ford never "updated" their TTY bolts for the 6.0. The only update I know of is replacing them with ARP (or similar) studs and most Ford dealers would do that if the owner supplied the studs.
Here's a picture of the coolant filter out of my 6.0 after a thorough flush. Thorough flush meaning a water hose running into the degas bottle with lower radiator hose and block drains removed while engine was running for 20-30 minutes on two or three occasions. Then filling the system with distilled water and a reasonable amount of Dawn dishwasher soap and driving for a few hundred miles before another flush, twice. Then filling the system with pure distilled, driving for a few heat cycles, draining and repeating two more times. Finally refilling with a 50/50 mixture of an EC-1 rated ELC. The picture of the filter is about 1500 miles after the flushing and refill. The red tint is from the ELC I used, the flakes are from the G05. Even with a full drain and pulling the block plugs on a 6.0, you still leave about 2 gallons of coolant in the bottom of the block. While some of that may look like sand, I assure you it is not or at least very little of it is. Sand does not mush out when you rub it between your fingers.
Here's a picture of what came out of the system on the first drain. Before any flushing was done. The truck was 10 years old and it was probably the first time the coolant had been serviced.