WD40 will clean, but it won't lubricate. MB uses a silicone paste lube there.

How to r/r the cabin air filter probably depends on the year and model of your truck. Including that information will help others to help you better.

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1973 280SE 4.5 (Sold)
1984 LWB 280GE (Sold)
2000 G500 NMLE - "Deep Throat"
2007 ML320 CDI (Sold)
2010 Porsche Cayenne S Transsyberia TipTronic (Sold)
2010 Audi Q7 3.0 TDI (Sold and Sorely Missed)
2014 ML350 BTC
2015 Audi Q7 3.0 TDI (On Order)