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While the box sump pan is off, while in there, you may as well change the oil filter and clean the tray magnet too. There's usually one in the final drive casing too. That's not a bad leak, just a bit of weeping. Maybe a litre every few years or so. I'd just do the fluid/filter/magnets and put it all back together- don't worry about the leak. If it comes out really dirty compared to the new stuff, might be worth changing it again in a couple of months; that's if you're gonna hang onto the car.

like @C3peteo says, can you actually move the selector out of park, through R to N? If not, could be the lock solenoid or ignition lock- nothing to do with the box at all.

If the box has run dry, it might be a gonner... But you could try refilling it with about 4L of auto transmission fluid. Auto gearboxes need regular fluid changes just like engines. EVERYONE ignores them... And both fluids. The output section takes regular gear oil, but the main section needs special auto trans fluid.

Have you checked the gearbox for a leak? Do you need to press the brake pedal to move the car into gear?