GM/Cadillac introduced the STS in Europe and the UK in '98 then basically deserted the people that bought that model.
The latest attempt to coax UK buyers to look at a Cadillac will not succeed unless GM and Cadillac do something to raise the corporate profile by a large amount.
Lack of support for the older STS has made buyers shy from spending £40k on a car that may devalue by £35k in 4 years (that's what mine did).
Think about how you treat your foreign customers, treat us like your American customers. Currently I know of only one dealership that will support servicing of my 2000 STS and they are at the other end of the country.
GM and Cadillac need to seriously raise their game to compete in the luxury car market in the UK and Europe. Until then good luck, you'll be needing it.