try putting some dry gas/gas line anti-freeze in there also. It will take out the water and won't hurt the seals. I was at a Myers dealer one day and they brought in a unit that was frozen up. After letting it thaw out inside for a few minutes they put dry gas in to get rid of the water. That was someone's fifty dollar lesson of the day, as I am sure they billed it out good.
Hyd fluid is hygroscopic. It will absorb moisture. You need to flush and change oil one time each season. The use of dry gas is not recomended by Meyers. Also replace the vent on top of res. I use k1 to flush out system as it will not harm the O rings and seals. Also use meyers or compatible fluid this is very important in hyd systems that operate at cold temps. There is no way of getting around having moisture get into system. That is why Meyers says to change fluid yearly.
my meyers used to freeze up also. i changed fluid every year. switched to automatic trans fluid. promblem went away. still change every year. costs $1.50 vers $5-$7. have been using trans fluid for 5 years now. no pump promblems. just my opinion that blue stuff not worth the headake.
In hyd systems fluid viscosity is very important. ATF is good hyd fluid how ever in real cold weather it is to thick, causes high current draw on motor which will cause motor problems faster than normal. We use Kendall Hyken Glacial Blue, SAE 5W-10. This oil will work well to -50 and costs less than Meyers. I purchase in 5 gal containers so the cost is less. Meyers also has a good phone line to call if you have problems. I live about 50 miles from them. If you have a problem call them they give you the straight answer first time.