Replacing rear speaker
 

My right rear deck speaker is shot on my 1991 190E and I need to replace. What is the trick in quickly removing the speaker? Done from within the trunk on or top? Thanks ahead

Easy
 

You can do it from the top....

Just unscrew 2 screws holding the grille to the rear deck, and then you can tilt and slide the grille out. Then, unscrew the corners of the speaker from the rear deck, and pull the speaker out.

I didn't notice if you'd changed the other speakers, but I'd recommend changing the dash speakers also. The front dash speakers come out in a similar manner to the rear deck speakers.

The speakers are "top mounted" but the screws holding the speaker grill can be hard to get at. I used a low profile ratchet driver with a phillips bit. Do it in the shade, since the heat through ther rear window will knock you out. The same low profile ratchet driver helps with the front speaker grills too.

BTW, you can use 6.5" round coaxial speakers in the back without having to cut any metal, just have to trim the rear deck holes to fit the magnet spider. To go 6 x 9 flush mount does require some minor metal cutting, or if you use a speaker riser, you could probably avoid cutting metal.