Beware of eBay sellers that have Model M keyboards that are pretty much thrashed.
My story is of an M13 Trackpoint II that was so bad, that I considered throwing it in the trash and forgetting about it.

When it arrived, I was shocked at how awful the keyboard felt to type on, even after cleaning it up.
I knew I needed to get a new cord for it, and ordered that around the same time I got it.
This is the original cable.

Anyway, after cleaning it up to the best of my ability, replacing the cord with a new one...

Most of the inside was full of RUST on the components.
A good example is the mouse PS/2 pass-through port....

This is what it looked like after getting it as clean as I could get it....

Of course the Trackpoint buttons would not respond at all, but the pointer did! *sigh*

I was at a point of being so frustrated with how it felt, that I knew it needed very serious help. The keys felt awful! The absolute worst feel of any BS keyboard I ever had!
I knew that I could just throw it away, and be done with it. But something inside me felt that it would be better to have someone more experienced than me that could fix it.
So I decided to get in touch with Maxx at Phosphorglow.
Long story short, the keyboard was run through a cycle on a dishwasher. Definitely not a thing to do with a Model M. It rusted the springs and the membrane needed to be replaced as well as the blanket.
http://phosphorglow.net/2015/05/27/130/Maxx literally had to rebuild the keyboard! He also fabricated new buttons for the Trackpoint. Once that was done, he also put the new mylar copper underlay.
It turned out to be a great decision. The keyboard is splendid now!
It was the best decision I made! I was very apprehensive because he turned that keyboard into what it originally was meant to be! Instead of looking good on a display case, it is actually usable and I am proud to have it!

So maybe it was the worst keyboard I ever bought. I'm glad I made my decision with it.