A cylinder leakage test will identify the reason for the low compression. Burned intake valve, burned exhaust valve, worn piston rings, and leaking head gasket are common. A small leak in the head gasket won't cause a huge drop in compression.
There's two causes for water in the oil. Condensation of humidity will cause a white cream-colored goo under the oil cap. That comes from a lot of short-trip driving and doesn't really hurt anything. It burns off on longer trips. A leaking head gasket can leak coolant into the oil drain passages or into a cylinder. In a cylinder it will be burned and go out the tail pipe as white smoke. In the oil, the level will go up and the coolant level in the reservoir will go down. Antifreeze in the engine oil can have very bad results. It dissolves the first layer of metal on the soft engine bearings. That leads to excessive clearances and knocking.
The definitive test is to add a small bottle of dye to the coolant. Later you search with a black light. The dye will show up as a bright yellow stain. If it shows up in the oil, it had to get there through a leaking head gasket or cracked head.
A cooling system pressure test can also be helpful. The engine might have to be at a certain temperature for the leak to occur. Look for a rising oil level or a cylinder filling with coolant.
Tuesday, January 17th, 2012 AT 4:02 AM