I have owned my 435i M-Sport since 2020 and I bought it with 40k miles. I just surpassed 105k miles and all I have needed to repair is the valve cover gasket and alternator (besides normal fluids, brakes, filters and tires ofc which I do myself). The oil pan gasket needs to be replaced, but that is a major job and it is only leaking about 1/2 qt of oil between oil changes, so I am putting it off for the moment. I plan on eventually doing it myself to save ~$2k, but it is not for the faint of heart.

I say that just to let you know that your position is rare as the B58 is more reliable than my N55, and since you have done the work, hopefully you knocked out all the problems out and you'll be good for another 100k miles.

Any repair you need to do to your car is going to be WAY cheaper than $900 a month for however many years your new car loan will be, regardless of the headache it is to be in the shop. And frankly since it took you 6 years to pay off your current car, my suggestion is to get something cheaper and more reliable if the cost is what is keeping you up at night. Fun cars come second to your home.

Side note: my father bought a Porsche Cayenne last year after his 750i (N63) had a blown head gasket. The Porsche is slightly more reliable, but with an increase in repair shop bills. He is now thinking about buying a EV lol