About twenty years ago, I bought a used IBM Model M keyboard with a PS/2 connector. I believe it cost me around $5-$10 plus shipping at the time. A good investment, given that this sort of keyboard is probably worth $100 or more these days.
Once about every 10 years, I clean the keyboard. This time I removed all the key caps I could and ran them through a dishwasher; that worked very well. The rest I cleaned with a damp cloth and a bit of dish soap.
After the cleaning, the keyboard looks really good. It was used when I got it, I used it pretty heavily for about ten years, and it’s now close to 30 years old. And yet it shows much less wear than the vast majority of keyboards of considerably newer vintage.
It’s obvious that IBM used a high quality plastic that does not yellow with age and is mechanically very resistant. The key caps are practically not worn at all.
The keyboard is probably just old enough to have been still Made in USA. To put it into perspective, it was made when Bill Clinton had been President for about six months, not long after the release of OS/2 2.1, and about two weeks before Windows NT 3.1 was released.
As with most old IBM equipment, don’t drop it on your foot. It’s heavy.
Given this keyboard’s track record, I would guess that in another 30 years, it will still be working fine, while most keyboards made today will have disintegrated into a pile of plastic dust.