Chickenlips Keyboard repair
 

Hi all,
I've recently picked up a Chickenlips A500 in a non-working condition, and spending some time getting it fixed. Parts for the mainboard are on the way (someone has made some REALLY ropey bodges on it previously, particularly on poor Agnus!) but one thing I want to tackle sooner rather than later is the keyboard.
It's the lovely hitek space invader jobby, however it's in a sorry state.
This is Agnus, being held aloft by blutac and some impressive yet odd soldering.
https://i.imgur.com/CQDx9X4.jpg
And this is the keyboard, after I've plucked all the caps & springs off:
https://i.imgur.com/sVrLEML.jpg
The metal plate is rusty as hell and I'd love to sand & repaint it, but more worrying is the PCB underneath. Now, I've unsoldered one of the switches to see how it all comes off, and it looks as if I'd have to unsolder every single switch. Not looking forward to that idea, especially without a solder gun! So, are there any tips for cleaning it up with the plate in situ? Thinking that maybe only an ultrasonic cleaner would do the trick as I can't get under the plate :( Manually trying anything with switches in place is hard as I'm likely to bend or break the switch contacts.
Any tips appreciated, even if it is "leave it alone!" - I know I have enough on my plate to get the machine working! :D

Whelp, no interest :( Well, I bit the bullet and did it.
Unsoldered every single key, learned a few tricks along the way. After about the 10th key thought about buying a desoldering gun! Persevered though and finally got there, and glad I did.
You can get an idea of the scale of the damage from here:
https://i.imgur.com/v1Dak0o.jpg
And in it's nude glory:
https://i.imgur.com/rVz3qgR.jpg
I double checked all connections and patched up the corrosion (it did look very much like liquid damage, likely coffee or coke) with nail varnish, as well as sanding down & painting the backplate
https://i.imgur.com/CVv9Oie.jpg
Very pleased with the end result!
https://i.imgur.com/9OmvAvA.jpg

Unfortunately I did find a couple of damaged contacts (one I damaged myself as I was learning how best to remove them!) so need to find a way to repair them, unless anyone knows of a good source of replacement switches?