Auto shop told me if tread depth of ONE new installed tire is different from other 3, then I'll get serious drivetrain repairs possibly as its AWD

Advice?
Pay $1300 at costco and replace all 4 tires??

 

This is usually a judgement call depending on how much tread is left on the other 3 tires. My 2015 GS350 F Sport AWD owner's manual says "do not mix tires of remarkably different treadwear." but doesn't go into more detail. If the difference in the new tire's tread depth is noticeable, but the old tires still have more than half of their useful life, I would only replace the other tire on the same end of the car as the flat tire. Of course a tire shop is going to tell you to replace all 4 tires regardless of condition. If you have a good relationship with your Lexus dealer's service department I would consult them for your specific situation. And let's see what the real experts on this forum have to say about this.

 

Depends on how thick the other 3. If they are already bald (or pretty worn) then replace all 4.

 

Its good that the shop told you this, because they don't want to take on the liability if down the road you have an issue. The drivetrain will be able to handle slightly different tread depths - the engineers have accounted for real-world situations that happen where drivetrain tires wear out faster or a misalignment causes tires to wear unevenly without blowing the system to hell.

Only change all four tires if the tread depth is significantly different. For instance, if your current tires are fairly low at maybe 3/32" or 4/32" and the new tire will be at a depth of 10/32", you may want to consider replacing all tires anyway. If you have decent tread left (6/32" or more) you can go ahead and replace one tire.

 

IMO, I would replace all four tires given it's AWD and depth is different or brand is different. I would shop around from America's Tire, Tire Rack and Costco.

I have a RWD model and replaced the Dunlop OEM ones with the Michelin Pilot Sport All Season 4. What a difference in ride, handling and traction but it's still expensive though.