I am going to do a coolant flush this weekend, I am having the same problem with the resivior tank and and the heat gauge. I am just going to do it myself because places want around $100 to do it. Plus, i like to do my own work on my car.
The oil looks fine, there is a bunch of gunk in the coolant resivor tho. It looks and smells like oil. I'm almost thinking that the lady that had it before me poured some oil into the coolant (usually I wouldnt think that but my sister dumped coolant into the oil on her car so really its not impossible.)Pull your oil dipstick and hope that it isn't milky colored!