Lea, I use Meg's clay and deep crystal system. Although I wax the SL quite often and wash it even more, I only give it an Autopian-style works treatment about twice a year. For this reason I have never gone beyond Meguiar's consumer range.
I used the clay to remove all of the tar stains, encrusted horse ***** and stubbon flies. It works amazingly well at removing this stuff quickly and easily. It's amazing just how speckled the lower body gets with this kind of difficult-to-shift stuff. I'm still on my first clay bar. You can use it with the detail spray or just with water as a lubricant.
I have used the deep crystal paint cleaner and polish, too. Again, these products have impressed me. They definitely hide very minor cosmetic defects and add depth to the paint. I find ScratchX better at hiding swirls, though. I'm not convinced I could ever get ride of all the swirl marks in my paint, though.
My spring clean routine is this:
Wash
Clay
Scratch X
Deep Crystal cleaner
Deep Crystal polish
NXT tech wax
Autoglym Extra Gloss Protection
Zymol carbon wax
I have found Meguiar's Quick Detailer to be an excellent way of removing dust and light dirt from my finish. I prefer it to Final Detail. On a regular basis I wax with NXT and do the "highlights" (eg bonnet, boot lid, wheel arches and waistline) with the Zymol. I went off the Zymol for a long time but think it tops NXT very well.
My wife can't stand me even washing the car, so normally I have to do some serious DIY before I can get away with it!
I would have thought you will save a lot buying a bulk order from the US. I don't know how customs duties are charges (try
www.hmrc.gov.uk) but I never had to pay any on my Autopia shipment.