Some good news at last. I saw a radio on Ebay at a breakers in London, the model number was one up from mine, an 86130 53172, mine is the 53171, the other number is NXF-9038ZT2, the original being NXF-9038 ZT.
I took a punt on it as he only wanted £199 posted and it arrived yesterday.
I've just pulled the two amplifier fuses, radio, ECU Acc and IG1 to deaden all circuits and fitted it. I then switched all the lights on and reinstalled the fuses. There was a nervy moment when one of the amplifier fuses drew a spark though, but it works! I've got everything back except DAB tuning, it says "No Signal" which is strange as the pre programmed stations work! Weird, but I can live with that. 😁
All the vehicle settings I had were retained, as were the phone book entries, even though I didn't transfer the contacts list.
Out of interest, Lexus wanted £6200 for a replacement unit, but offered £3100 back if I exchanged the faulty one! That's funny, as she started off by claiming they can't be repaired.
I'll also be trying a small claims court against Lexus, I can only lose £30 after all.