One of the most endearing traits my Grandpa had, which I happily inherited, was his ability to stay 
(my Grandpa; had; the most endearing traits my Grandpa had, which I happily inherited) (the most endearing traits my Grandpa had; happily inherited; I) (One of the most endearing traits; was; his ability to stay)
my Grandpa the most endearing traits my Grandpa had One of the most endearing traits
had happily inherited was
the most endearing traits my Grandpa had, which I happily inherited
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his ability to stay