You may discover that water in oil is caused by a cracked plunger or a failed plunger retainer o-ring rather than the crankcase oil seals.
This is correct, however you can replace the oil seals without breaking down the crankcase. Remove the plungers, take an old, worn flathead screwdriver if you have one, turn the pulley until the piston is all the way back, insert the screwdriver as shown. It doesn't have to be in this exact spot or position, it's just an example, but the main thing is not to scratch the piston rod.
At this angle, turn the screwdriver clockwise to hook the blade under the oil seal, then rotate the pulley. If you need to come in from the right side, turn the screwdriver counter-clockwise. The shoulder of the piston will push the screwdriver up and should pop the seal out with it. It might take a few tries and repositioning the tool, but it does work. When you install new seals, be careful the lip of the seal doesn't roll out - oil the seal and it shouldn't be a problem. A piece of 3/4" PVC makes a perfect seal driver, just drive it in firm but gently, the seal retainer will press it in correctly.
You don't absolutely have to replace the oil seals, but I always do because the spring inside the seal is steel and will rust, plus while you're already in there it doesn't hurt.
You'll need to replace the copper washers, o-rings, and backup rings. The copper ones are only meant to be compressed once. It's very unlikely there's a cracked plunger, but it does happen.
43367 - Plunger
43235 - Backup ring
17399 - O-ring
45891 - Washer
I use a mix of 3:1 of the cheapest ND oil and transmission fluid to clean the water from the crankcase. It's an old mechanic's trick and works really well. Change the oil every 2-3 days until it stays clear.