Number 11:
First, the gurgling noise is "normal." I have a 1989 300TE and it does make a gurgling sound. I think there was a Benz service bulletin on this issue. It is not a big deal.
Second, only you can decide whether it is cheaper to keep her. A lot has to do with your financial situation. I would get an estimate for fxing the things that are most urgent/necessary. Then compare that to the cost of a new car--interest on a loan, higher insurance, higher registration fees, etc. I thinkt hat you will find that the cost of repairs is usually always cheaper than getting a new, or even a used, car.
Third: A lot of the cosmetic issues, like broken door handles and bad upholstery can be taken care with a trip to the locay "junk" yard. You may find just the parts that you need. If you are handy with a wrench, then you will be OK repairing or fixing things.
During part of my college career I drove a POS Ford Maverick. I hate it that car, but I kept it going until I could afford something better.
Take heart, the W124 are very durable and sturdy cars. If you do not believe how tough these cars are, take a look at this:
W124 Torture Test
My 1989 300TE (like the one in the video) has over 210k miles )it has gone around the world more than 8 times) and, except for a tranny overhaul, I've not had to spend a lot of money on it. My son will "inherit" the 300TE as soon as he turns 16 and gets his driver's license.
Good luck!