Just done the same mod - here's a pic having done one side... thanks to Andy for the writeup!
You can now get the whole resistor inline package from Amazon for £15 - http://www.amazon.co.uk/resistors-Decoder-Convert-computer-message/dp/B007O7JVTI/ref=sr_1_fkmr1_1?s=automotive&ie=UTF8&qid=1367675449&sr=1-1-fkmr1&keywords=382+LED+error+free, then stick in ordinary LEDs. Or there are a couple of LED suppliers that say they have built in resistors - but they're £20 a pair, and I figured if I ever needed to replace the bulbs, I'd rather just do it with vanilla ones.
I bought these bulbs: http://www.amazon.co.uk/gp/product/B0093VHTCY/ref=oh_details_o00_s00_i00?ie=UTF8&psc=1 (£9)
and 2 of these resistors: 10R HS 25W Arcol Aluminium Clad Resistor (£3)
and 4 of these Scothlocks: Scotchlok (£2)
plus a couple of bits of 3A mains cable stripped out of the protective sheath. Works a treat!
