Thank you Vince - just the info I was looking for. There is some evidence on a few of those mounts that I tried to use something similar the last time I did the job. I was thinking of using double sided trim tape, but that might make it tricky to line up the nubs. The plastic welder sounds like a better solution.

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Len
'59 220S Cabriolet-SOLD and living happily in Malta
'83 240D 351,500 miles original owner-SOLD
'88 560SL 41,000 miles - totaled and parted out
https://sites.google.com/site/mercedesstuff/home
'99 E300 turbo 227,500 miles
'03 SLK320 40,000 miles - gave to my daughter
'14 Smart electric coupe 28,500 miles
'14 Smart electric cabriolet 28,500 miles
'15 Smart electric coupe 28,000 miles