Thoughts on case corrosion?

[nigelUK]

A trusted collector has mentioned to me he has a 1680 with some heavy pitting/ corrosion that he would sell to me for a good price. Currently his daily beater and would be my daily beater if I decided to go ahead.

It has a nice dial/hands and the rest of the case looks ok.

My questions to you learned folk are . .

is corrosion terminal ? (The watch originated from a very hot country & assume sweat would have been the main catalyst - and that source is now removed, I live in the UK . . we don't sweat)

Presumably Rolex would not carry out a movement service without case replacement due to warranty issues / water resistance ?

Are genuine movement parts impossible to come by for 1680s should I require them further down the line ? (and want a service by independent)

See photos below ;
Note: I think the photo indicates a bit of corrosion in the rehaut area ?

If the collector sees this thread please do not think I am picking the watch apart !, I'm just seeking additional advice / info on the corrosion.