I was trying to get a new crankshaft pulley so checked out Ebay, etc for prices. I'd already checked servicebox and confirmed the xu10j4r uses the same pulley as the xu10j4rs (0515k6), so ordered a shiny new j4r one for £38. They sent me the wrong part (for a 1988 Renault Espace?!) but when they checked my reg number they said I needed a totally different pulley to the one I ordered, which cost.... £89! Much arguing later I've finally got the correct part coming for the advertised price, but a £51 premium for saying it's a "GTi6 part" is somewhat steep!
I then did the same for a cheapo 3rd party rear silencer and noticed the 3rd party part numbers for the j4r and j4rs were the same (and looked the same too) but had a £60 price difference! The cheaper 'cheapo box' fitted just fine, of course.
I've also noticed similar smaller discrepancies for various other 3rd party bits and bobs through Ebay, etc.
Now I know there are differences between the two engines - basically anything from the top end is different, but according to Servicebox 90% of the other parts are identical, so it looks like 3rd party parts manufacturers (esp on Ebay) have realised they can charge a huge premium for GTi6 parts purely because it's a 'performance' engine.
What a rip off!