IBM Model M - key causing double press

[zeigerpuppy]

I have a 1984 Model M keyboard, which has been a happy typing friend for quite a few years.
The only thing I have serviced is replacing two key caps and a foot pad, never even opened it.
Lately, I have a problem with the "0" key on the number pad.

When I press the key, it often (but not always) will cause a double press, outputting "00". 
If I were in finance, I may see this as an advantage, alas I work in data science, so it's not so desirable!

I have tried removing the cap and using some canned air to clean the switch, but it hasn't made any difference.
Any tips on what's the next step?
I'm not scared to do a teardown, but not sure what would be the best thing to try next to get the key working properly again.

[E TwentyNine]

You don't have to do a "real" teardown.

If you open the case and look at the bottom of the keyboard assembly where the numpad is, you're probably missing some rivets there.

The easy fix for that location is to take a piece of paper and fold it a few times so when the assembly is put in the bottom part of the case, it gets squeezed between the case/paper and the little hook in front that holds it down.  Don't put too much paper as you could potentially snap that hook if you try to jam it all together.  Something like a thin piece of sponge/foam may work as well.

You just want a little pressure on the bottom of the plate to make up for the missing rivets.   

[zeigerpuppy]

Thanks for the tip E TwentyNine,

I'll give it a go and report back!

[zeigerpuppy]

I had a look inside today, cleaned up the dust and tried pressing/bolstering the area around the numpad "0".
The inside looked pretty good, even all the plastic rivets were in place.
However putting pressure in that area made no difference, so I guess it must be a problem inside the switch itself.
Unfortunately looks like replacement keyboard time...

[E TwentyNine]

Well...the next thing I'd try is to reseat the cap.  Pull it off, lean the keyboard forward (almost vertical) and put the cap back on.

I might also swap the spring out with a less used key, that's a little trickier.