Unless there is something different about your engine, I can’t see how a leaking head gasket could cause coolant to get to the the plug hole. Maybe a crack in the head would allow coolant there.
Often the plug hole is surrounded by oil in the rocker cover and a leaking seal will let oil get to the plug, but not coolant.
Are there coolant pipes running near ...
Were the heads decked (checked and milled perfectly flat) when you last had the head gasket replaced? This indicates that they weren't, and you'll never get a good seal if there is any warping on the heads.
Does coolant fluid in the cylinder well indicate gasket failure again?
Indeed it does! Or it may also mean that the original problem was not actually a head gasket. The next likely causes are warped or cracked cylinder head or engine block.