This may not be strictly true....
C
warranty or unsaleable , once it becomes well known that it's an expensive potential problem it's going to make getting out of one quite difficult unless you're PXing
If I were looking at one in a private sale that hadn't been done I'd either want it doing or it'd have to be at the right money to offset the risk
It's OK saying it hasn't happened to me , it's happened to at least 3 members on here plus Richard grace has advertised a few that have been done so it's a potential problem that needs looking into.
I'm not saying I wouldn't buy one that hadn't been done if it was mint and at the right price but a CAT C with a potential 4K bill would need to be very cheap as you'd be stuck with it forever , not saying it's a bad place to be stuck like