Thanks for the info - everything is documented at the dealer. I've written to LGB arguing that:
1. That Lexus Sidcup failed to exercise reasonable care and skill in rebuilding the engine, causing damage to the components described above; or, alternatively and without prejudice to the first argument, that they failed to exercise reasonable care and skill when removing the components by not identifying that they were faulty.
2. Or, that as Lexus Sidcup claims, the faults were present before the engine rebuild and so are therefore covered under the warranty because they have prematurely failed.
3. Or, that these components too suffer from design or manufacturing defects and have prematurely failed.
I also told them if they don't fix it then I'll get the vehicle forensically examined, with the hope that the vehicle examiner will show that the components are either defective, prematurely worn and so generally "not fit for purpose." I realise this will cost me a lot more than just getting the DMF replaced and it's a gamble that I'm right, but a car needing £10k worth of repairs in three years is frankly ridiculous... I had a clapped out rover whilst I was a student that I sold still working fine with 150k miles on it.