Hello and welcome to just answer,
Sorry but I'm not sure what it is you are looking for.
Someone at the "shop" will have to inspect and repair the leak. Epoxy, silicon and other magical potions wont work on repairing the vehicle.
If the frost plug is leaking then it must be replaced, if the intake is leaking then it must be resealed properly. It is not very difficult to pressure test a cooling system and locate the source of the leak.
If these guys can't do this for you the you should ask for your money back and go somewhere else and they should change profession because this is obviously not working for for them.
As for the misfire, they probably ruined the spark plug
wires, coils or spark plugs.
Some of these items have to be tampered with while replacing the lower intake gasket and if they weren't removed properly (damaged) or reinstalled incorrectly they will cause misfire.
Also they will need to check for vacuum leaks.
It amazes me that reputable shops go out of business while incompetent others have work.
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