Yes 90W is going to be too heavy, especially in cold weather. The hydraulics will move very slowly. But it will work until you get the problems worked out, just in case you have to drain it to work on it.
I would also be concerned with the cleanliness of the bottom of the case. To my knowledge there is no filter on the pump intake. Since there was water in it, there's probably rust falling down from where the water condenses above the oil level. All you can do is clean it best you can, vacuum and blot it out before refilling it.