.........probably why you have the complaining power steering fluid pump is that someone (not saying you, but....) someone has been filling it up with NON Benz fluid. Must flush all that old bad stuff out, turning steering lock to lock with the engine running, sucking the old fluid out with your wife's (or significant other's) turkey baster. Make sure and remove the filter from the reservoir before doing this. It'll take quite a bit of fluid to get all the bad stuff flushed out sufficiently.
Get on the net, order, say, 3 containers of fluid and use them all for you need to run this removal process several times (start engine after removal of filter turning steering all the way right and then all the way left then center it and remove the fluid in the reservoir, refill and then do it again and again and....well, you get my drift).
autohausAZ will have the fluid AND the filter. www.autohausaz.com or somesuch.