what type of oil in a motor/pump - Joe K.

Joe K

I opened a motor today and some light brownish oil spilled out. Its a motor with a propeller on it. Its not a heating motor, its actually used in an automatic pool robot cleaner!! The motor drives the propeller which pushes out the water with a force strong enough to push the robot across the bottom.It runs for about 2 hours under water before it automatically shuts off. It actually turns on and off every 30 seconds to reverse itself and I was wondering what type of oil to replace it with and I figured the experts on here would have a good idea :) thanks