Martin, in my experience (like yours) the email link to UK DS has never worked either.
Turnaround time is now much quicker than it was - orders are fulfilled in 7 to 10 days of paying for them, sometimes less.
And Caroline is as helpful a ever.
The time for spare parts to be available used to be for 10 years after a set was withdrawn and then was reduced to 7. It may now be shorter with the increase in the number of sets issued each year.
I certainly can confirm it's worth asking for parts from sets withdrawn more than 5 to 7 years ago - you can have some pleasant surprises - but people should do so sparingly. No one likes to input an order or deal with requests where out of, say, 25 items all but 2 are not available as they feel they have wasted their time and, more importantly, been unable to help the customer.