I bought my 530 under similar conditions as it was supposedly overheating but it turned out to be just a bad temperature sender. I had begun to do my homework as to what is required to change the head gaskets. First, you need a special Torx socket ($25) to get to the head bolts, which need to be replaced (one time use, $40), then you need to buy a cam timing tool ($160 on Ebay if lucky) to hold all 4 camshafts in place while the TDC is set and the cam sprocket bolts are tightened. Prepare to spend at least $400 in gaskets because the head gasket set (about $180), get this, comes WITHOUT the head gaskets which are about $60 a piece and is also missing the 22 rubber grommets ($22) for the valve cover nuts. I got the gasket set since my car was leaking oil very badly and needed to be done anyway.
Which brings me to the point, is he sure that the miss is a head gasket? In this engines when the valve cover seals go bad, oil tends to accumulate in the spark plug area and if it gets bad enough, could short the coils. Coolant loss could be the infamous valley pan gasket, which you can no longer get by itself as you have to buy the pan with a sealant bead on it (another $75). I would do a compression test and have the cooling system pressure tested to locate, confirm the leak. it could even be the water pump seal!
Last edited by jimoreno; 07-14-2009 at 12:38 PM.