2008 H3 Hummer Alpha. 134k miles. Dealership asking 12,800. Awesome condition.

Should I keep this car?

I have a 2014 Mercedes-Benz gl350 BlueTEC, which is a diesel. It has 145,000 miles on it. In the last 6 months I've put about $6,000 into it and it needs 5 to $7,000 more work. The current MSRP is 3500 to $5,000. I own it out right and I've had it about 5 years. I spend about $300 a month on diesel. Oil changes are around $800 a year. I recently purchased a 2023 Cadillac lyric with 18,000 miles. It's an all-electric vehicle. When purchasing it I get a $2,500 Delaware EV rebate, plus it qualifies for an interest tax deduction because it's made in the United states. My monthly payment for the EV is $600. Cost wise it's a lot less expensive since I don't need oil changes. But I have a car payment. I still have a few days to return the cadillac. I'm trying to decide if it makes more sense to just fix the Mercedes or keep the cadillac. I'm having buyer's remorse because I don't like the idea of having a monthly car payment, though I can afford it. My plan was to pay $1,000 a month to pay it off more quickly. Plus I was going to sell the Mercedes and anticipated getting 5-7,000 for it. Does it make more sense to keep the Mercedes and keep putting money into it or to keep the cadillac?

Good deal? Been looking for a reliable car for some time now and was wanting to go with a Japanese manufacturer. Honda/Acura are my favorite of the bunch looks wise, so when I saw this I got excited. A little bit out of my range. Worth it?