After my recent 2013 RX350 inspection my Lexus dealer tells me I have a leaking R/R shock and should keep an eye on it. They quoted me $390 + tax to replace and do an alignment. I asked if this was for both rear shocks and was told just the one that is leaking. My questions are should the rear shocks be replaced in sets? Is an alignment necessary? How many miles should I expect rear shocks to last? I drive about 8K/yr.

 

That is robbery. You do not need an alignment after replacing the rear shocks. Yes, they should be replaced in pairs, especially on an 8-year-old vehicle. By your estimate you have about 64000 miles.
Shocks can fail at that point and the OEM rear shocks are a known weak point that is prone to leaking and failure, sometimes after only a few years. You got a longer life than most from your rear shocks.

Any independent repair shop can easily replace both rear shocks for a lot less money. Look on Yelp or Google for a reputable local independent car repair shop. This is a simple job that even a gas station repair shop can perform.

OEM rear shocks are easily available online (or maybe at your local dealer) for between $36 and $50 each!
https://www.google.com/search?q=2013+rx350+oem+rear+shocks&rlz=1CAEVJI_enUS901US901&oq=2013+rx350+oem+rear+shocks&aqs=chrome..69i57j33i22i29i30.7916j0j7&sourceid=chrome&ie=UTF-8

There are good aftermarket replacements available from KYB for a little more money.
The replacement is very simple as there is one bolt at the top and another at the bottom. It should take less than an hour.

 

The rear shocks are a weak link on this truck as they are prone to leaking. They should always be swapped in pairs but even if that wasn’t the case I’m sure the other one will be leaking pretty soon. They are extremely easy to swap and any mechanic will do this job in under an hour. I’ve never done any suspension work ever and it took me an hour to do both. Really only about ten minutes per side once the car was up in the air and the tires were off.

 

Thanks for the imput/advice. I think I'll continue go to my local non-dealer guy.

 

Did the 65,000-mile service on my wife's 2015 RX350 FWD this morning. While I had the wheels off for the tire rotation, I inspected the rear shocks as well as the front struts. No leaks anywhere, and the suspension continues to perform normally (no complaints from her, anyway). A local Lexus master tech who has proven to be quite honest with me told me a couple of years ago that Lexus addressed and corrected their infamous leaking rear shock issue before the 2015 model year. This may indeed be true - time will tell.

Whenever shock replacement time finally rolls around for this vehicle, I still intend to go with the Bilstein B6 products.