How old is it? Can you verify that with receipts etc?
The 280L is from the Nepton line.... which comes with a 5 year warranty.
Typically, AIO liquid coolers are warranted for their expected lifespan - 5 years is about what you can reasonably expect from any decent AIO. By their very nature, they're not going to last indefinitely.
The Nepton's launched in ~2013 or so (IIRC). If bought new at the time, you're right at the 5 year mark and I wouldn't spend any money on it.
I would suggest, if it was bought within the last 12-24 months (and you can get proof of this), then it's probably a decent cooler for $40.
If it's any older, I would avoid.
Remember, the MSRP at launch was $139, shortly thereafter was reduced to $120. So...