Thermostat gasket slight leak
My car has 49000 miles.
My car has an automatic transmission.
There is no real way to give you a definitive answer unfortunately. A small leak can remain a small leak indefinitely but it can also turn into a major leak in a matter of moments with no warning. Because of that possibility, there is no real way to say "it’s ok to drive XXX miles with a coolant leak". .Any coolant leak should be addressed as soon as possible. Coolant loss will cause the engine to overheat and possibly lead to engine damage.