Save the Dell PowerEdge blue indicators

I deal with dell servers extensively and have never come across this. (Various ages from new to 12 years old) All seem to be uniform for me across various sites.

Something that might resolve this or at least point out the source of the problem is to use the cabled UID/Status-Indicator that comes with Dell cable management arms. They plug into a small socket on the back.

The LEDs behind those lights very rarely break and they generally don't fade.

What you're experiencing is a dust problem. When fine dust accumulates along the light pipes the dirt eats up the light. You should keep your servers in a dust-free environment. Alternatively, clean them regularly.