A lien on a vehicle is covered under IRC 6323(b)(2)
You do not have to pay the $25000 prior to selling but you do need to turn over the proceeds to the IRS.
(2) Motor vehicles
With respect to a motor vehicle (as defined in subsection (h)(3)), as against a purchaser of such motor vehicle, if—
(A) at the time of the purchase such purchaser did not have actual notice or knowledge of the existence of such lien, and
(B) before the purchaser obtains such notice or knowledge, he has acquired possession of such motor vehicle and has not thereafter relinquished possession of such motor vehicle to the seller or his agent.
It protects the purchaser from having the lien follow the vehicle. This is true as long as the buyer is not in a position to have known about the lien. This is important because if property transfers to the buyer with the tax lien attached to it, the IRS may have the right to seize the property from the buyer. So under IRC 6323(b)(2) the buyer is protected.
Here is a link to the full IRC about this subject
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