Got my replacement used turn signal lenses in today and the drivers side lens separated from the housing. Anyone here have any suggestions on the best type of adhesive to use for this? I really do not want to replace the damn signal for a third time!

I believe they are made from ABS plastic. This is also what black plastic sewer pipe, and plastic model cars and airplanes (Revell kits) are made from. Try ABS solvent type adhesive (check your local home improvement big box) or model cement (check with your local hobby store).

It is not a true adhesive but really a solvent that dissolves the plastic. When you push the joint together, the solvent evaporates and the dissolved plastic hardens to complete the bond.

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The OM 642/722.9 powered family
Still going strong
2014 ML350 Bluetec (wife's DD)
2013 E350 Bluetec (my DD)

both my kids cars went to junkyard in 2023
2008 ML320 CDI (Older son’s DD) fatal transmission failure, water soaked/fried rear SAM, numerous other issues, just too far gone to save (165k miles)
2008 E320 Bluetec (Younger son's DD) injector failed open and diluted oil with diesel, spun main bearings (240k miles)

1998 E300DT sold to TimFreeh
1987 300TD sold to vstech

That seems about right. The plastic seems to have been meted an glued together from the adhesive.

Plan of attack is to sand the stuff down, put the adhesive on and use blue tape to hold it together for a day.