Ok, one thing I learn't early on is sometimes you need to cut your losses to avoid going backwards.
Some cars will be absolute money pits where you spend hundreds every month in order to keep it running. You could use this money instead to purchase/pay off a newer/better condition car which doesn't need work, just normal maintenance.
If it's just a minor gearbox issue and everything else on the car is great (or already fixed or parts replaced) then it would be worth fixing and keeping for a few more years.
If however there is a lot that needs fixing then it would make more sense to just put that money towards getting a car in better condition.
Remember also that lots of issues can crop up in the future, especially after a car is around 10 years old and over 200,000kms. Things like radiator, ABS/Electronic modules, air con, suspension, water pump, headlining, things that seem minor but can cost a bit of money over the long term.
Of course, the other side is once you have fixed everything it's generally good to go for another 5 years without many issues.
You have to decide for yourself. However if it was me and if this IS the same car as in your other thread with all the issues, then I would get what I can for it and find a replacement.