I still have my original Citadel D-lock which I purchased new in 1979 for £34.99. That was a lot of money for a lock back then, but it came with a guarantee of bike replacement (up to the value of £1,000) if the cycle was stolen whilst locked with the Citadel. Even so, I got it at a discount as it was a sample sent to the professional cyclist, Keith Berry, who owned Thatto Heath Cycles in St. Helens. He knew I'd put it through its paces. It has been on every bike I have ever had and out in all weathers and left overnight in areas of London, Liverpool, Naples, and elsewhere.
There have been several attempts to cut it but non got past the outer plastic coating, although they cut through the so-called Squire "high-security" lock that I had on the front wheel. The Citadel has survived attacks by saws, angle-grinders, and long bolt cutters. One attacker evidently got so frustrated that they let the tyres down! They were Kevlar Continentals.
The Citadel is on my main bike and I wish I could get hold of more of them as I still consider it outperforms the Oxford and Kryptonite locks I have on my other bikes.
If you have one of these then cherish it. They don't need much in the way of maintenance.