-Last Night - for son's recent $750- 2003 P5 purchase, I removed and replaced both rear struts at 155K miles.
Driver's side was making "thunking" noises when hitting bumps and when pushing down on left rear car body.
-Struts purchased are Duralast struts from Autozone.
Duralast Loaded Strut Assembly LS53-90822L
Duralast Loaded Strut Assembly LS53-90822R
--Maybe not the best and definitely not the cheapest but pressed for time.
--Also didn't know I could have ordered them online and saved 20% with a discount code and next day delivery.

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STRUTS
-Before removing the struts, I spray-painted the bolts, the struts outer outline, and empty hole of the lower strut mount against the spindles (didn't have a Sharpie) to verify and maintain the new strut's alignment.
-The old struts had a super thin transparency paper plastic "strut mount gasket" installed on the top of the strut and between the wheel-well body to act as some kind of cheap (my guess) vibration isolation damper.
-I used that clear plastic gasket to make my own gasket using foil-backed rubberized "peel-and-stick" waterproofing membrane material, (stuff normally used on roof valleys and edges, and when installing exterior doors and windows) - at least twice the thickness of that plastic gasket) and installed it (stuck) it on the top of the new strut as a vibration (noise) damper.
-Why - Because I had a 2000 Maxima that had no strut mount gaskets at all and it was noisy as hell until I pre-fabricated and installed some improvised gaskets (back then used regular general purpose gasket material and they worked well).
--FYI - Mazda dealerships sell strut mount gaskets for a few other Mazda models including the P5 for about $2.50 plus shipping. Below is a link to a Mazda dealership where you can find them and other parts.
2003 Mazda P5 Strut Mount Gaskets
-I will test drive the car later today and report back how the struts sound and work after installing new brake pads all around (rotors good), Exile shift linkage bushings, and a Megan short (throw) shifter today (weather permitting).