My '06 GS-430 has just under 80,000 miles. The rear end is really soft, rides rough, rear tires are cupping, and the car seems to bottom out on bumps, especially if I'm making a left turn when I hit a dip (i.e. turning into my driveway).

Tire guy says it needs new struts. After calling around, it looks like this is going to be somewhere between $900 and $1400 depending on where I take it. The struts are Lexus dealer only - no third party equivalents seem to be available.

Has anyone had this experience? Are struts serviceable or do they have to be replaced. Am I getting sucker-punched here?

Sucker punched? More like Donkey Punched!

I assume you don't have the air suspension setup? "I don't see them as options for strut replacements".

Go to www.parts.com. Drill down to your car, 'rear suspension' ~ 'components' ~ 'struts'....
$204 a piece. I assume these are probably the correct ones, as they only list one type. And at $200 a pop anyway, I would have to assume they're "adaptive".

Buy them online, take them to an indi mechanic to install. Probably $600 out the door "$400 for parts, $200 for install for both".

I'm not sure I'd be comfortable ordering these...When you call the dealer for parts, they ask for the VIN number because there are actually 7 possible struts for that car. My car does have adaptive suspension - I guess...there's a button that allows me to switch to "Sport" mode.

If you didnt want to go through the dealer my advice would be to go to someone that just works on Toyotas and Lexus. I googled 'lexus repair dallas' and these were the results . Just go through the results, call around, search the companies name then review into google and see if anything bad comes up.