So I managed to speak to someone in Lexus parts and asked if it was a common part requested. He says Lexus doesn’t have frequent issues, but he does get asked for this part semi frequently and it could be considered one of the most common issues. He didn’t know the exact causes, but suggested age and others thought that pulling down on the boot rather than use the electrics causes the motor to over heat and fail.
he also corrected our part number (why is it so hard?!?) to 68910-48023 for our 2012 (61 reg) rx450h
We tried Lexus and other parts companies, but they all stated a 3-4 week delivery time (obvs coming from UAE or US). So we’ve gone direct with amayama (part from UAE) and hopefully saved ourselves some money (£300 inc delivery, but likely need to pay VAT and customs), despite not saving ourselves any time
best of luck with anyone else going insane with this issue. Hope the above info helps someone