To update this story.
I took my XE into the dealership today for its 21,000mile/2yr service and, while it was in asked them to look at the rear shock absorber leaks.
Unfortunately, I have a 50 mile journey to the dealership and there was torrential rain nearly all the way. This meant that all traces of oil were washed off the shock absorbers, so off course the dealership could find nothing wrong with them.
They also clearly didn't believe that I'd found a patch of oil on my drive directly below the driver side rear shock absorber - and that the base of the shock absorber was "wet" with oil, saying "they'd never seen a shock absorber failing like that". Neither have I, but I'm pretty sure I wasn't imagining it, though after a protracted discussion with the Service Manager I'm beginning to doubt it myself! They also said that a "misting" of oil on the whole shock absorber is quite normal and not a fault - and they assured me that they had wiped my shock absorbers clean for me!
So, I am really no further forward. I'm going to keep an eye on these shock absorbers and if they continue to leak I think I'll just replace them myself to avoid any further hassle with the Dealership.
BTW - the 21,000 miles service cost an eye-watering £529 and it was completed in less than 2 hrs. Labour was £224, parts & oil totalled £213.74 and VAT was £87.55. Within the parts cost was 7L oil at £121.66 and cabin filter at £49.08, both with VAT still to be added.
I know dealerships have got to make a profit, but some of these prices do seem to me to be well over the top. The car will be a year out of warranty when the next 2yr service is due and I think I'll do it myself then!