Definitely ask. I always make the mb salesman aware when ordering that if it goes up it’ll stay fixed but if it goes down I’ll expect it to be matched. They’ve always agreed with a “why wouldn’t you?” attitude.
The AP on my BMW dropped £100 after I ordered it. As it was such a small amount I didn’t bother to ask them, especially as they’d already given me £500 off the AP and 15% off the optional extras, but they called me to say that they had done it anyway without me even asking. The comment was “better in your pocket than Motability’s”.