I would pay no more than US$5,000 for that car. As many have said before me, you'll need to drop another $1000 or $2000 just for fluids, and other things that will break on a 15 year old car.

I estimate a head gasket job will cost you $3,000.

Can you do some of the work yourself? If you can, then get him down on the price. If you are not a DIY, it will be an expensive ride.

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1989 420 SEL