Re: I am astonished
I drove one of those for about 9 months.
I had 8 or 9 of them over the years. I was doing insane mileage, so although I was averaging 35,000 miles out of each, they didn't last me very long. But that's not bad for cars I was generally getting for about £200.
the bodyshell would rot every time a bit of water touched it
Yours had been crashed.
Citroen had built themselves such a bad reputation for rusting with the CX - an otherwise lovely car - that they did something about it with the XM. To make them rust meant fracturing the zinc layer - and that's a fairly significant prang. None of mine had any rust, despite the fact that I didn't exactly take fantastic care of them.
 The depreciation on these cars was unbelievable. The cheap ones were almost £40K when new in 1990. I was mostly driving them in the late '90s. They'd usually cost me £200 to buy the car, and I'd get between £150 and £200 when I scrapped it some months later :-)