Original sentence: Ease of replacement depends on accessibility.Expanding rubber plugs are available as replacements when access is a problem.Freeze plugs can often be a source of troublesome leaks as a result of internal cooling system corrosion.In many cases the plug area will be difficult to reach and using a mallet to perform maintenance or replacement will be nearly impossible without special facilities.The sand casting cores are used to form the internal cavities in the engine block, usually forming the coolant passages.They are a subset of the plugs on a car engine cylinder block or cylinder head
Edited sentence: The sand casting cores are used to form the internal cavities in the engine block or cylinder head(s), usually forming the coolant passages