450C Transmission

[lsts]

My machine sat for several years before I recently bought it and the other day I decided to change all fluids on my 450C crawler dozer before I started using it. When I pulled the drain plug on the transmission I got not only the oil to drain but several gallons of water. How is it possible for water to get into the transmission? Is it possible to get water in the tranny from sitting out in the elements?