Ladies Datejust Crown fell off - Need Help

[madaboutlawns]

Hello all,

I've been reading the forum for a while and have finally decided to tackle my wife's watch problems.

It's a Ladies Datejust, I'm guessing late 1980's. The case says 69000A. (SS) with 18K white gold in the bracelet.
The crown went missing around 2 years ago and it's been sitting in a box ever since.

I got a couple of cheap watch fixing tools delivered today and I've started to have a look at the watch.
So, case off - Pin in the release button for the crown and winder and crown pin out.
Now, I need to know the crown size to order and where to order it from, so that it'll fit the tube. I'm guessing a new crown will just screw into the old pin? Also, once the crown and pin are remarried, will I just slide it back into the watch and screw it all tight again?
If anybody needs any more details, I can find them.

I'd be really grateful for any help and advice.
Thanks