Another answer is at http://www.ukwhitegoods.co.uk/modules.php?name=Content&pa=showpage&pid=217
which is a link from the (also helpful) page at
http://shop.ukwhitegoods.co.uk/Washing%20Machine%20Parts/Bosch/Bosch%20Door%20Seals/BS18101%20Bosch%20Washing%20Machine%20Door%20Seal%20Gasket.html
These are hits further down from the search I suggested in my previous reply a few minutes ago. It all looks do-able, though a bit scary unless you're quite good a DIY. I'd certainly not go out during at least the first wash cycle to chek that it doesn't leak!!
Mike (again!)
September 2009