sir. if you want, you can have the problem estimated with your trusted mechanic. I think he wouldn't tell you to replace the tranny if it isn't really needed. You might not know, the cost of the repair might just be playing around the 5 - 7k mark ... much cheaper than a surplus tranny and definitely much cheaper than a 2nd or brand new vehicle.

if your mechanic suggests you to change your tranny, might as well change your engine too. It`ll cost you at around 50-60k depends on the engine that you prefer. I find it better too than selling your current vehicle and replacing it with a vehicle that's as old as your vehicle too. Of course, you wouldn't know the vehicle that you're buying has hidden problems that might lead you to costly repairs or that's even worse than the problems that your current vehicle is encountering now.

but then again, it's still going to be your choice.