The car will run fine without the belly pan, that is mostly for sound encapsulation and to protect from road debris. But you don't really need it per se. Spark plugs can be purchased anywhere as long as they are THE RIGHT TYPE. The flex disc is about $60 to $80 if I'm not mistaken; click on "Buy Parts" above and you can price it for yourself. It's not so much the parts that cost on a flex disc replacement - it's the labor.

I buy most of my parts here, to support the site. Just think of the free advice you are getting from people whose only intention is to help you (not milk you for cash). Fastlane can usually get me the parts next day.

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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