If you can find a seller that's close to you (same state), has a long warranty (months not just days), and has a good reputation (high and many positive feedback ratings), I wouldn't hesitate to purchase a used EHA on eBay for less than $75. It only takes a few minutes to install. They either leak or don't. Make sure you get a NEW set of real EHA o-rings with it. Do not re-use the old ones unless they are less than a year old. The new, improved material for them (I'm told, anti-Ethanol) is colored light green. The original ones are dark green. They are an odd size and can not be found at the local hardware store or auto a/c shop. Of course, they have them here at Pelican.

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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