mike,if you think about it running on petrol preduces carbon which protects the valves to a certain extent,lpg is hotter and remove carbon from your engine(valves)over time,hence the damage to some engines over a very long period,i've had two ls400's converted to lpg in the past and both required certificates for insurances purpose's, and a new certifacate had to be issued after so many years,but your right sbout about the ls400,it has hardend valves and dosnt require flashlube,i've been humming and harring about having my lexus gassed, think i might bite the bullet and go for it