What do you base that scaremongering on ?
The use of a additive kit ( Flashlube or better still VAP valve saver ) will ensure many miles of trouble free motoring. I can show you a Lexus RX 350 with nearly 70000 miles of gas use and no valve problems.
I fitted LPG to my 2003 GS300, in less than a year (50,000 miles) it twice burnt the valves out and yes it did have flashlube fitted, cost me a fortune and ruined a good car. Previously ran a V6 Omega on LPG which covered 200,000 with only some dramas, but Lexus engines don't like it. Never again for me but hope you get away with it, my engine would not idle on gas nor re start once stalled meaning I had to get out and push it off the road and often would cut out at speed, lane 4 of the M25 is hard to forget! Cost me many times what I could have ever saved and I was caught between the LPG installer and Lexus both blaming the endless faults on the other.Complete nightmare !!!