When it was hot, did you notice any boiling heat from radiator bottle?
Anyhow, the gasket can be arranged but i've noticed its better to swap engine than to undergo the hassle of repair.
Obviously, you must have the water level in radiator to the full by topping up again and agian after some time. Already you got your radiator serviced. Believing no more blockage.
Listen, blockage could be anywhere apart from radiator so listen if coolant hasn't poured yet as its costly. Mira has 3.1L of coolant, open the bottom plug for draining then when the water stops coming out, try to use the pipe of air which is generally use at service station or in workshop for cleaning air filter to blow out the water from the hoses. Check and tell us if the air comes out from bottom plug forcefully to be acertain that there's no blockage in system.
Were you using tap water before which may had caused the rust and resulted in blockage. Sometimes green coolant as well results in generation of rust and blocks up. similarly, pink and green coolant shouldn't be mixed.