That is a scary situation. The best, and cheapest, thing you can do is immediately replace the gasket. You can keep driving it with a slow leak, but you will have to keep putting Transmission Fluid in it. Which will cost you more in the long run. If you replace that gasket now, You won't have to worry about constantly re-filling the transmission fluid.
by replacing the bad gasket / seal
Transmission filters are INSIDE the transmission. You need to remove the transmission oil pan. When you replace the filter, plan on replacing the pan gasket as well.
You need to buy the specific gasket, its plastic not spongy like other gaskets. I guess it will run about 50 bucks. Remember to get the right gasket or else it will leak
yes, make sure you clean surfaces on block and gasket before installation
Buy a new transmission oil pan gasket before your transmission blows from leaking liquid.
By replacing the whole gasket.
It is located in the transmission, only accessible, by dropping the transmission pan, not very hard to do, but lots of bolts. The transmission filter is located within the transmission. One has to remove the bottom plate of the transmission to access it. A filter usually comes with a new gasket for replacing the bottom plate, but be sure you do.
It would be recommended if coolant had mixed with the engine oil before the head gasket was replaced.
Yes there are sealers out there that can be used to seal or repair the gasket
It will be on the bottom of the transmission
It requires replacing the head gasket.
It could, if the old gasket had failed.