acf,
I pretty much "double up " these services, for ex:
Coolant, Diffy, -every 15K for sure,
Maybe every 15K - Brake flush (if I'm in the mood)
Trans fluid - I do a pan drain/ refill (approx. 2 quarts of t-IV) & SYNTHETIC OIL CHANGE @ 4-5K!
Since I'm a DIY'er, I can follow this schedule for only $120-30 a year (or what a dealer would charge for 2 oil changes.
Parts:
Check lexus-parts.com also for comparison.