5.7 liter "R code" engine in a '99 K-1500 GMC (a professional rebuilt long block, installed about a year ago) by a trusted mechanic. I have been struggling with an unexplained and intermittent loss of coolant for some time. He never found any leaks, but recently he took it back to recheck and he told me that this time he put a pressure tester on it and found a few hose clamps were in need of tightening and that may take care of it. I drove my truck home (2 miles). The next day I went out to use my truck, but before I started it I checked the coolant and oil. For the first time ever (I change my own oil, every 3,000 miles since the motor swap, and I always have clean oil, ALWAYS!!), I found a "coffee milkshake" looking sludge on the dipstick. I did not start the truck. Instead, I got under the truck with a clean jar and slightly bottom-drained about 4 ounces out of the oilpan. It looked the same as the dipstick. I took it down to the shop and showed it to the mechanic, and he is going to take care of dealing with the remanufacturer, HOWEVER, in the midst of our conversation, (Being a former mechanic myself) I expressed my concern over having antifreeze mixed in with the oil, primarily for the sake of the engine bearings. The reponse I got was that Dex-cool antifreeze is different, it doesn't harm engine bearings if it mixes with the oil. I am looking for some insight about this because I'm just not sure I can buy it. I have searched the web and found (much to my dismay) a lot about Dex-cool and law suits, class action suits, gasket damage, intake leaks, coolant in oil, etc. I must say that most of what I have read is about the GM V-6 engines. I did not see (yet) anything about the 5.7 or any other V-8 engines. Any information that you could pass along would be greatly appreciated.