Not Much, Really.
Amazingly Reliable.
Timing Belt, etc., were replaced around 90,000.
Brakes replaced twice, but hey, it's a 12 year old car.
Sun roof rusted and was replaced while still under warranty.
Only real problem ever was with the rear window regulators ~ Replaced twice under warranty and once since the warranty expired.
One dealer told me that since '96 was the introductory year for the RL that they had a few problems with the window regulators.
LOVE, LOVE, LOVE this vehicle.
My first sedan (other than a BMW325 in 1986) ~ Mostly I've driven all sports cars Mitsubishi 3000GT, Nissan 300Z etc.) so when my job dictated the need for travel and more space, I was very reluctant to purchase a sedan, hence the reason for a used one at that time.
Some people say this ride is sluggish and big ~ NO WAY. Granted, I can't do what I would do in a 300Z, but this car's handling has been phenomenal. I am (unfortunately) a born speeder, this is a fast, smooth and sweet ride with easy, easy handling and lots of room.
Finally, now that it's 12 years old, I'm starting to have a few maintenance issues, paint on the roof is fading and the seat foam is disintegrating so these once comfortable seats aren't as great.
I imagine if I had ever garaged it, the paint and the seat foam would be in much better shape.
I did have an accident and the car sustained a tremendous amount of front end damage. I was fine. It looked like the car had been driven off a cliff. The bodyshop owner said that these RL's hold up better than any vehicle he's ever seen ~ Designed to take the impact so the driver and passengers don't have to.
The only reason I've kept it so long is because I like this Acura "look" (like the old Vigor or Legend) better than the new "rounder" RL. Keep hoping they'll bring it back, but so far, no luck.
Window regulators are a common problem on the Acura RL. Two of them were replaced on my car.