I never found the vaseline stuff in any of mine.
The main things I found over my few DexCool cars were that it is more like half-set jello. It does feel greasy unlike jello, but it was never that vaseline consistency. I have found vaseline in water jackets where there was a previous head gasket failure. Seems like any oil that got into the coolant gets gelatinous over the years and hangs out in the nooks and crannies.
I put an intake manifold on a 454 and put a little smear of silicone around the water passage in the gasket. Before I knew about the evils of Dexcool, I decided to use some because a friend gave it to me. A month later I had to pull the manifold because the machined pad where the distributor sits had been machined to far causing an oil leak and Edelbrock had sent me a new one.
The black silicone I used around the water passages had seeded a growth of stuff that looked like orange rock candy. When I pulled it off, it was slimy like Flarp (that slime stuff kids play with) but also had super fine grit in it and the rock candy structure was more like Knox Blox (those jello finger foods where you add double the gelatine). In just one month it had closed off that passage by probably 1/4 of the cross section.
That's when I started researching DexCool.
The verdict is kinda questionable on the Vortec engines, but they used a silicone imprinted intake manifold gasket, and the assumption was that their frequent intake manifold coolant leaks were due to that same seeding from DexCool.
Most coolants have silicates in them as silicon compounds (not to be confused with the above mentioned silicone... a whole different animal). They are suspended in solution and usually don't cause any trouble, but the OAT (organic acid technology) used in Dexcool does not use silicates and is far less stable at holding the silicates in solution. Since your engine is made with a sand casting, its full of silicon. If they precipitate out, again, no worries. The silicates themselves aren't the problem. The larger issue is that those silicates are then reactive once they drop out. In GM's case, they almost always use clay tablets (with silicates in it) in their cooling system. Its an old-school trick. If a small leak develops, the clay plugs the hole. Its one penny of prevention that might prevent GM from paying warranty repairs. The clay in the tablets doesn't play well with the OATs in the Dexcool. The downside is that no amount of flushing will truly ever get all the clay out of the pores of the block.
Dexcool itself isn't necessarily evil, but its fragile. If you have a brand new block and use distilled water, you might get lucky, but expect trouble. Dexcool is remarkably good at corrosion protection. The Silicates (a combination of silicon, oxygen, and one of a bunch of possible metals like boron, potassium, manganese, aluminum, and sodium) are more electrolytic and can cause more corrosion. No silicates = less bimetal corrosion.