Water in Oil

My 340 was rebuilt about 3 years ago, barely has 500 miles on it. I pulled it to rebuild the front end and paint the engine bay, that spiraled into a full blown resto-mod mod

It was storeid in my insulated garage, bagged. It had 5 qts of VR-1 10w30 and whatever coolant in the block, that wasn't drained when the motor was pulled.

Fast forward to tonight, I was ready to put the motor back in and when I drained the oil, the first 3 seconds or so was pure water (not coolant green, clear water) then the oil started flowing.

I drained it all out and then pulled the pan, cleaned it and the pickup. I peeked up at the cylinders and they all looked perfect.

I know the water was the oil breaking down along with the temp changes, but my question is what should I do to prevent this happening again before I fire it up, which probably won't happen for at least another 6 months, maybe a year. (Being realistic.)

Thanks for any help. Sorry for long post. Here are some pics of the install.

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