As you know while the speakers in the 123 are a standard size: 4" or 10cm, they are cut away on 2 corners which makes fitting any aftermarket speaker a nightmare.
Here's what I did in the front:
I purchased some lower-end coaxial Pioneer speakers with only 4 tabs and screw holes around the perimeter. After removing the MB speaker grille and speaker, I used a utility knife to CAREFULLY slit just under the "lip" near where the cut aways are on the MB speakers. Make the wire connection, Start from the rear (farthest away from you), work the speaker into the hole and slide the speaker's tabs into the slots you made with your utility knife. Line up the "rear" holes, sink those 2 screws, and you're done.
All in all, a pretty tight fit. I'm not experiencing any rattling of any kind and with the MB grilles back in place, nobody's the wiser!
I'm going to tackle the rears next!

I've made an attempt to remove my front speakers & gave up. I didn't see any screws in the speaker that attached it to the dash bracket from the top. Did I miss something? It seemed that the speakers were almost glued in place??

Thanks-

85 300D 236k

Your car may be different. For mine, there's an odd shaped grille in each corner of the dash and flush with it. There's only one screw holding the grille in. I removed it and saw the speaker underneath, secured with 4 screws and with a funky metal "cage" protecting the fragile paper cone on the top (this metal is literally part of the speaker and cannot be removed from the speaker.
It certainly can be frustrating when you want some decent tunes in your car and cannot get access...
In my 533i I put some Infinity's in that I got on clearance...only problem was that they stuck up about a half inch higher than the factory grille! I ended up buying longer screws and 1/2 inch spacers so that I could still put the factory grilles back over top!

Shawnster,

I can't imagine why you would want to replace your speakers!
They just seem to get better with age. Mine sound terrible, especially with the tape player. They cut in and out, sometimes I hear all four speakers, sometimes no more than one. What's next? You're going to suggest upgrading the stereo itself? That's just crazy! You can't buy the kind of character a twenty year old automotive sound system can provide. Let alone, the anti-theft value. Who's going to smash your window to grab that state-of-the-art, push-button Becker?
And the look you get from other drivers when you pull up at a red light in your old Mercedes, with Alan Jackson or some Merle Haggard blaring through the open windows on that crappy old sound system - Priceless.

And you want to replace it?

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Dave
1995 C280
1999 Triumph Daytona 955I - my speed fix.
1982 300TD - Gone, but not forgotten.

Shawnster,
I did the same thing with the front speakers over a year ago and everything seems to be holding up pretty well. I want to replace the Pioneer 4" speakers I replaced the OE speakers with and I guess I'll have to find new speakers that have the same 4 tab design. Be careful. If all you've done to your stereo is replace the front speakers, you're going to get really carried away soon. I started out with the front speakers, then replaced the headunit, then replaced the rear speakers with 6.5" speakers and re-wired everything, then I added a sub in the trunk. You don't know what you've started.

Alex

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1983 300D (parked for four years)
2012 VW Sportwagen TDI Manual
2001 Miata SE
1962 Chevrolet Corvair Rampside