What kind/how much of a common engine fluid/oil will slow/stop an engine oil leak when added to the oil.?

There are many additives sold in auto repair shops that claim to help stop leaks. A common remedy is going a grade thicker on the engine oil. BUT this is quick fix until the leak is fixed. Whilst these quick fixes may work they might cause seperate issues (even damage) down the line especially running a thicker grade oil. Unless you have no plans on keeping this vehicle for a long period of time then fixing the leak itself is always preferable. Also there may be an underlying reason that caused the leak in the first place which may require urgent attention.What kind/how much of a common engine fluid/oil will slow/stop an engine oil leak when added to the oil.?
Best is to find source of leak and repair or replace gasket.