Not trying to hijack thread but I have a similar question. I've been looking at a 1973 Eagle 8V71 with slight coolant in oil pan. Owner claims it is an injector tube leaking and he has had this happen before on other engines...Is this a possibility or is it more likely to be liner seals?
Check the chassis for rust. A "slight" water leak is a subjective term...means different things to people. Anyway, the water in the engine may be the least of your concerns if rust in the frame is found. Get EXPERT help with Eagle rust! Do not guess at it. If frame passes inspection, let the owner repair the water leak.. since he knows what it is
...then verify that it is fixed.
You may have any number of things leaking...pretty much rule out liners though. Engine would have to be inframed if water has been leaking into it for any time. I'd run away. With a bad engine, a 73 Eagle wouldn't have a lot of value...unless it is unusually nice? Do you have a place to park the bus and work on it? Can you pull the engine? Unless you are very well equipped to repair the engine yourself, or can change it out, my suggestion would be to get accurate estimates of repairs for leaking engines...
Brian's situation is a little different with a known good running engine that has been exercised recently, and apparently has not had water mixed into the running engine.
Brian, if you pull the heads, may want to have them serviced while they are off. You may find a crack in one of the heads. Sammy offers a good idea with pressurizing the cooling system. Close off the heater cores before you perform this test. No since in testing the heater cores tolerance for pressure.
You may see the fizzies...this would be good to note where water isn't, as well as where it is. Once you pull a bearing, you'll know whether you need to replace or leave the bearings.
Good luck, JR