To Change PS Pump, What Else Should Go Along?

[Jay11]

2003 C240 87k Miles, new addition to our garage, mainly parked for the last 3 years.

New to MB, not to wrenches under the tree. Looking to replace a whining PS pump. I am wondering what else should I get together with this?

When you start the car you can hear it whining for sure. The whining doesn't change in volume consistency or in any way at all. Shop said it was it - during a PPI (but looking back they missed a few things and I am not sure that I can trust their word.) I would like to establish that it is the PSP that's the issue. So how do I confirm that it is PSP that's whining?

What is a good brand to get? Should I get it with or without a reservoir, pulley?