2002 civic ex intermittent starter failure temporarily fixed by the removal and installation of the same starter

My daughters car started out having intermittent starter failure last week. she
said it would work after a few tries. a day later it completely quit, turn the key
and it clicks once. i checked the battery tried to jump it with a corded 200A
starter box- nothing. i checked the internet, saw the rubber bumper on the
clutch- still intact, pulled the starter, took it to the parts store to test it- works
fine. reinstalled it and it worked. I turned it on and off 5-6 times no problem.
next day daughter takes it to school and back home and when she went to
got the work, problem has returned. no wear and tear on the harness that
would explain it, i didn't open the harness. I did notice a bad leak oil from the
cylinder head plug- leak fixed and cleaned up, reinstall same starter and
starts no problem, lasts for maybe 10 starts and then same problem. i intend
to thoroughly clean the block with a scour and hope it's so simple. any other
advice is welcome. if i can figure out how, i will update after the scour pad
idea. it'll beat least a day before it stops working again