Well, I got the leaking heater valve out of the car and found it is an "updated" type. Identical to the older type except for the valve arm which has a peg sticking out of it and is slightly longer than the older one which just has a small hole in it that the cable fits in. Phoned my local Eurocarparts place, and found that a replacement is £50 (includes taxes and delivery). I've placed a small towel up under the mount for the valve, even though the leak is minimal (small bead appearing every few minutes with engine running) until the part arrives which should be Wednesday.
I was looking at the FCP Groton site you U.S. guys have, out of curiousity and found that the price there is $14 !!!!!! Even if that is the older part, that still costs £25 here without adding tax or delivery. We may be able to buy Volvos a lot cheaper secondhand, but we pay for it with parts !!!!

$14 = £8.12
£50 = $86.08

For more or less the same part !!!!!