Can't tell you much about the seat repair piece or repairing springs, but I will tell you the pool noodle trick WORKS. Be sure to buy various sizes and shapes of pool noodles - they have round ones, flower-shaped ones, etc. and also different diameters. You'll find it helpful to have a variety to stuff into the odd shaped recesses of the seat springs.

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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