It is a common issue. Mine had burnt a hole through the leather when I bought the car used, and I noticed it would get very hot a couple days after I took the car. I complained to the used car dealer and got the driver's seat bottom replaced through a contact of the used car dealer at a BMW dealership. I was told to go to said dealer to find said person and they would take care of it. A couple hours later, I got a new seat bottom that works perfectly fine, with no questions asked or anything. They somehow fudged the paperwork so that it was covered under warranty, yet my car was not a CPO and was out of the standard BMW new-car warranty. I'm just happy I didn't have to pay anything.

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2006 BMW X5 4.8is - Black Sapphire/Cream Beige
2001 BMW 330i - Alpine White/Beige (retired)