Sound like a common issue with the RL models. Here is a post from the past of a member having the same issue. It seems it will be a real PITA to try and isolate the problem/s that is causing the warning light. Here is the thread:
So this is what a VSA is"
VSA stands for "Vehicle Stability Assist." An onboard computer monitors various stability factors. If it detects an event such as the beginning of a skid, the computer instantly responds by controlling the engine rpm and the brakes to correct the condition
. The VSA system can be overridden by depressing a button on the dash causing the VSA icon to remain lit indicating the system is not active."
VSA Light and Traction control (NO FIX)
I hope you find the problem and fix it...
Here is another review from another site that had similar situation with their 04 TL.
"I have a 04 TL the VSA light and warning light started coming on at various times a couple of weeks ago just like you described. Sometimes the VSA light would come on at start and I could not get the car to come out of park. So I started thinking oh god tranny....
Went to the dealer today and they found that my battery was only producing 390amp vs 550
and my brake switch was going bad
(hence no drive). Fixed in 2hrs."