Recently power steering on my 98 E320 hesitats when turning left. it does not make any noise but when I turn the streeing wheel to the left it feels like it does not want to turn but after a second or so it realease it and turns. There is no shaking. I tried to check the steering fluid but could not find the resevior. I found a tube with a black cap on which say MB only.

I appriciate any input.