I have a 2003 monte carlo LS 3.4 I bought about a year ago with only 75,000 mi. I try and do most of the minor repairs myself. (Oil changes, radiator flushes, drain, refill, change plugs; you get the idea. Three months after purchase, I serviced the car. I changed the oil & coolant, replaced the coolant and I noticed a rusty oily sludge around the top of radiator cap, not really concerned at this point because the car was performing GREAT! I thought it was the previous owner's poor maintenance. I went thru with the oil & coolant replace, all was fine. I drove the car about six more months, changing oil at regular intervals. It was purring like a kitten, then suddenly when I crank car after driving it 30 miles to a store, it sounds like a loss in compression almost to the point of shutdown. I got the car home and started looking around under the hood. I noticed low coolant in resevoir and then opened the radiator cap. Again there was rusty, oily sludge(maybe a little more this time). I checked the dipstick. No milky residue, drained coolant and was clear. Have gotten many "diagnosis, guesses". Mostly being the intake gasket and head gasket. Also, I am getting very wide differences in repair estimates. Any thoughts, ideas would be greatly appreciated at this point! Thank you!