I have the non bosch versions off fleabay (just wanted a cheapo version to see if I liked the design), they have worked perfect so far with no issues. I can only remember one member (his uncle I believe) who had one fly off, so not really a huge problem or design flaw as yet I may get bosch next time just to see if they are any better, but would go back to the cheapo ones without hesitation if the bosch ones weren't worth it.
From what I remember, halfrauds didn't list any for the Mk1 GS300 either, but they did fit, maybe they would fit the RX as well. I went for the flat type which halfrauds didn't do anyway the next time round.