Please check the compression, especially in 5th cylinder. There is problem with 5th cylinder on gs300 & gs350 second generation. Some investigations shows that the problem may be because of faulty sealing of air engine filter. Sand and other dirt is mixing with oil, making abrasive, that destroyes 5th cylinder. I don't know is there is replacement campaign for this problem.
FINALLY they got my gs300 in the shop they rebuilding the motor. now I want to no do I have to pay for certain parts because the lexus dealership told me I may be responsible for certain parts like oil pump an stuff. but I don't see how I would be responsible for that cause its all part of the engine too me , but correct me if I am wrong