I fixed the nets in my W126 by removing the plastic side rails as indicated above, then purchasing $2 worth of black elastic cord readily available from the sewing section at Wal-Mart, from fabric stores, etc. Took about an hour and the nets look like new!

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08 W251 R350
97 W210 E320
91 W124 300E
86 W126 560SEL
85 W126 380SE Silver
85 W126 380SE Cranberry
79 W123 250
78 W123 280E
75 W114 280