So now I remember how to do this, as I struggled with it for about 15 min wondering how the heck to wedge anything in that tiny space behind the firewall and where the filter cover sits. THE KEY is the clip that's holding the filter cover closed is at the BOTTOM, closest to the firewall. IMPOSSIBLE to fit any tool in there. You have to stick ONE strong finger in there, reach slightly behind the clip, and pull down. The first time it will require a couple tries as the clip is tightly held on.
How do you get your hand in there? You CAN remove the glove box and bottom glove box trim panel (2 parts), but that's annoying with all the screws. HOWEVER, if you're not overly huge or big, it's doable by pushing the passenger front seat all the back, laying on your back, removing the bottom trim panel below the glove box (pops off by pulling down on it). In this position, the clip will be above your left shoulder and the retaining clip will be above you (rather than at the bottom). Shove a strong finger into that ridiculous tight space and pull.
Once you do this once, it's possible to not even have to lay down and get to it next time. I "bent" back the retaining clip enough without breaking it, but loose enough to ensure it comes off with light finger pressure. If your hand / arm isn't too big, you can reach through the glove box access panel to get to the filter cap / filter. Now I understand why the 13 MY SL I owned previously was much easier...the clip was already loosened and i could simply pop it off with light pressure.
germang33k wrote: ↑Fri Nov 15, 2019 8:26 pm
No way it's a 10 min job

I had to get the Autozone guy to help me remove the glove box after I removed all the screws. Now I can't get the filter door off to save my life. It doesn't just pop off or unclip like in all the videos. Can't get a screwdriver or any other tool in that tight spot to wedge anywhere to loosen the clip or cover. I am also not clear it's the top or bottom of the cover that unclips. I can't believe I have to go to a mechanic to remove the stupid filter cover. I've changed cabin filters in Hyundais and Kias. Way easier!