Replace both bearings?
 

Was told the right front wheel bearing on my '05 RL with 200K miles is going bad. Was quoted $450 to replace.

Should I have the left replaced as well?

Nevermind---I'm changing all four!

Usually I always advise replacing suspension components one axle at a time (at a minimum), but it seems like you're replacing all 4 :)

Replaced all four wheel hub/bearing assemblies on my '05 RL with 203K miles yesterday. Went with Timken from RockAuto. Front right and Rear right were grinding. Now quiet as a church mouse, and car feels like it has much lower rolling resistance. I wish I'd have recorded accurate MPG before the switch to see if it bumped up.

Lessons learned:

1. Pneumatic impact driver at 120 PSI saved the day! Tried and failed with breaker bar. but could not crack the axle nuts. even with a long cheater pipe. They were a b#*@h!.
2. Use two 8mm x 1.25 thread pitch bolts in the 2 threaded holes provided in the rotors to slowly push the rotors free from the hub---worked like a charm. After repeated failed trials and errors to free the rotors from the hub,, made a trip to Home Depot to purchase the bolts, and they made all the difference.
3. Used a wheel puller to pull the hub off of the spindle of two of the units in which the splines had become rusty and stuck to the splines on the old bearings.
4. Be sure parking brake shoes are in perfect position before reinstalling the rear rotors. My left one was askew, discovered when I heard a "clanking" sound as I backed down the driveway. Found the left rear brake shoe to be misaligned.
5. The fronts were quicker/easier than the rears-----ability to turn the steering right and left made for better access, and the hub bolts on the rear were much harder to get to and fiddle with.