Birt, Brian's comments are right on. One other source is a cracked head. I had a cracked head on a WD and the antifreeze ended up in the oil. When I pulled the head, two of the pistons had antifreeze on the top of them (pistons were dished). I suggest that you find some place like NAPA to have the head pressure tested.
More comments on the seals. Check them out very carefully when you remove them from the sleeves. Look for cracks in the o-ring or general deteriataion. You will need to put in new ones as these are not expected to be reused. They aren't very expensive - generally about $5 each. Email me if you need a source. Clean the seal point for the sleeve with a good solvent. Using 220 or finer wet or dry sand paper, clean up the sealing surface. I usually use a cylinder hone to get them smooth - the cleaner and smoother, the better chance of a good seal. After you have cleaned them up good, do the inspection looking for anything that would prevent a seal (for instance - a crack - most likely between the cylinders). If you find anything suspicious, I'd have the block magnifluxed (NAPA or someone can do this for you) just to make sure. The crack may be so obvious that magnifluxing is not warranted - you need a different block. If things look good, and if the o-rings looked suspicious, you can reassemble the sleeves with new o-rings. There are proceedures for putting these in that minimize potential damage to the o-rings. Email me.
Before reinstalling the pistons, I recommend you hone the cylinder walls. If you aren't changing the rings it will help reseat the rings. If you are changing the rings, it is mandatory to get the new rings to seal. If you don't have a hone and don't want to buy one, you may be able to rent the hone from an auto parts store like NAPA or Autozone.
You aren't over your head. You are just learning a new skill!