Do shocks have a limited 'shelf life?'
 

A friend and I both bought our R53s at about the same time, mine an '04, his an '05, both with sport suspension. At delivery he had the dealer remove his shocks and springs and replace them with JCW components. The removed parts went into a box in his garage. Twelve years later I bought them from him and then acquired the remaining parts necessary to assemble complete strut assemblies. All the parts I bought were OE or the equivalent. Last year at 155K on my original suspension components (except for PowerFlex LCAB) I installed the 'new' assemblies. I am not happy with the result. Seems harsh: curb cuts, cobble stones, etc are extremely unpleasant, unlike my memories of the car when new. So my question is: do shock absorbers degrade simply by virtue of the passage of time? Soon I will start replacing other remaining original parts - ball joints, sway bar bushings, etc. - and then get an alignment, but not if the culprit is more likely the old new parts that I used. TIA.

Shocks, over time, get softer as they degrade, not harder. I will say that 12+ year old shocks were probably not your best choice because seals do dry out and harden. I have the sport suspension on my 2004 R53 and it's really stiff even after installing the new Bilstein B4 shocks.

Take the shock out and compress it manually, without the spring. If it comes back up slowly it’s probably good. Stock shocks are rough anyway.

I did similar - bought a cheap set of takeoffs years ago. Went to put them on last summer, and no joy. Not sure if it was just age or because they were stored in a hot shed, but all four were pretty much toast.