The gasoline has likely varnished the inside of the FD making unsuable, or it may have even rusted the inside if the FD if the cast iron version. You can take your chances with finding a good used one around $300 (make sure to match the part numbers) that has a decent warranty. Used onse are just as old as your car though and may not last very long. If you are planning on using your dad's car and not just getting it ready to sell, seriously consider having it rebuilt for around $500 or a newly rebuilt one for around $600. eBay has some really good options. If you do a lot of homework, have the time to invest, are methodical in your approach, and are very, very careful, you could try to rebuild it yourself. The kits cost around $100.

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03 CLK430 Cabrio 211K Pweter Silver/ Oyster Leather
90 300SEL 214k Pearl Black/ Alto Grey/Black Leather

Prior: 85 190E, 88 300TE, 89 300TE, 90 300E 2.6, 90 300TE, 92 300E 2.6, 91 and 93 300SL, 87 Ferrari Mondial Cabrio