rear plate coolant pressed in fittings
 

what does 1 do when corrosion has eaten them?
any1 know of a source for these parts?

They're not sold as individual parts and doubt there's much of a market for anyone to be making them. The heater hose outlet can be removed with a soft drift and hammer (when used judiciously)....so you could scavenge one off a secondhand plate. The 10mm barb, you'd have buckley's, but it would be a 5 minute job to turn one up in a lathe. Near zero chance to remove without drilling out I'd expect!

The small one on rear iron I drill out and tap a 1/8th gas thread in it and screw a barbed fitting in it