Thanks to all who contributed to this thread. I completed the jobs under the 300TE. After shopping around I purchased original mufflers from the dealer. They are Gillet brand on our 300TE (my 190E has Eberspacher). With my club member discount the price was actually less than some after-market suppliers and not much more than copies of unknown quality. I fitted the new mufflers just prior to our concours where the car picked up a class win (W124 & W201 class). I did not have time to fit the flex coupling before the concours due to being busy cleaning the car. I found that it was easy to replace by removing only the transmission mount. The front section of the driveshaft could then be pushed back sufficiently to remove and replace the coupling. I did not have to remove the exhaust or anything else and the job was completed in very short time. I purchased the coupling from an after-market OEM parts supplier for little more than half the dealer price. The new coupling had identical markings to the original with the MB part number and star ground off.

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107.023: 350SLC, 3-speed auto, icon gold, parchment MBtex (sold 2012 after 29 years ownership).
107.026: 500SLC, 4-speed auto, thistle green, green velour.
124.090: 300TE, 4-speed auto, arctic white, cream-beige MBtex.
201.028: 190E 2.3 Sportline, 5-speed manual, arctic white, blue leather.
201.028: 190E 2.3, 4-speed auto, blue-black, grey MBtex.
201.034: 190E 2.3-16, 5-speed manual, blue-black, black leather.