Just got a 94 deville concourse need input

I love my new "old" car. We just got from my uncle's estate. It has 139K miles on it but when he bought 2nd hand the dealer told him the
engine was replaced at 80K miles. The tranny went up 3 years ago and was replaced with a rebuilt one. The only problems we have are cosmetic. the pull down visor on the driver side is detatched and there is this squeak that sounds like it comes from the driver side back passagner seat belt.
Is there any advice to give to this new car owner as to maintenance and care?
I love the gas mileage on it. we average 28 hwy and 20 city. thats better than my 2003 ford taurus.
Thanks Lisa

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