New car, well used or previous retention

Hello, Since our Polo 9n 1.4 Diesel, Bj 2003, has a few problems, I wonder if I should still put money into the car, or if I should buy a new/used car. The Polo has some electrical problems (costs about 600€), some bigger rust spots, until half a year ago he also pinched while steering in and the rear silencer has already lost its outer shell. The question is now worth investing in the car? (in 1-2 years would have to be due to K I had a Seat Leon FR in mind, but as an EU import (should be unproblematic, shouldn’t it?) or rather a well used one in Leon size. Shouldn’t you be a petrol guy, because I only go to university and sometimes to my parents/in-laws. I could find up to 20k €. Which of the 3 options would you recommend me? Greetings