Hi,
all cars have problems, my RX300 had a transfer problem at 45K, Lexus Sheffield quoted around 2k to fix, gearbox specialist in Doncaster did same job for £479.
I would wager if Lexus has quoted £350 for fix you wouldnt have even turned your PC on, its just that its always 1k plus at Lexus, thats why they can afford beautiful showrooms, excellent coffee and service, and why you always get a luuurvly courtesy car.
Like all main dealers not just Lexus they just change out probable parts until its fixed, do your best to stay clear of them when possible, Do some deep research on clublexus, over 400 000 RX300 sold in the US, so if it can go wrong it has gone wrong and chances are its on clublexus, the Americans do use some slightly different terms to describe certain things but its very self explanatory, also you can just join the club its free and post your exact problem!
Cheers Jason