Power steering quits

[scottsubarus]

Power steering quits at times. First noticed it when first starting car cold, in very cold weather. Steering hard and sluggish (no squealing noise) It acted like GM racks do when cold out. After a minute or two it snapped out of it. BUT, a few days later and after driving car with no problems, I was driving and started a turn when (agahst!) NO power steering assist! had to muscle it through the turn. After sitting for 2-3 hrs, went to leave and P.Steering was working fine. I noticed the next morning P. Steering fluid(trans fluid) was leaking out the front of the car....raising the hood to ck the level and source of the leak, I noticed it was coming out the secured cap on the P.S. resevior and running down to the ground. Fluid level seemed full. Any ideas??? BTW, its been sub zero cold here.

Scott
Omaha