I dont think anyone mentioned this yet, but pay for a pre-paid inspection (PPI). About $150 at a local Indy familiar with BMWs. The seller should allow this, if not walk away. The shop can look into the oil pan leak. The price seems fair considering the mileage and yes, you can buy an extended warranty from a BMW dealer and cost is around $1800 to $3000 depending on the timeline, car status, and coverage. FYI...you can also handle some of the maintenance yourself, if you are not mechanically inclined there are many DIY's in this forum. A good way to learn and will save you $$$
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