Well believe me when I say I tried EVERYTHING before I got to the right thing. I looked at:
Final E in grid in clues, Final Y in grid and clues, Final ly in clues, Things that went on or lasted forever (like Pi, the Messiah, Dvorak symphonies, characters voiced by Mel Blanc),
PI19DCircumference / diameter
[--] and
PIE35AClosed-topped fruit pastry
[---] RA and
SRA (since you seldom do two letter answers I was suspect), Words with "ON" in them to see if there was ON and ON.
FINALLY (yes, reference intended) I went back to my forever idea and while looking up the half life for scandium (and finding it to be hours instead of eons...stupid non-radioactive isotopes) I went back to
SCANDIUM40AElement with atomic number 21
[--------] again and instead landed at
SANDPIT28APlayground feature involving buckets and spades
[-------] . "Idiot" I proclaimed, but I saw how I could do that since it had an AND in it....WAIT A MINUTE NOW! So there were a preponderance of ANDS, plus they were symmetrical; clever boy Ben. Of course my first answer AEPOIMIL (which Webster's defines as "Inability to solve a meta crossword despite having the right idea") was wrong but "ultimately" I saw my way home. Now here I was going to say, and finally - and then go on for another paragraph or two, but instead I'll just say "Thanks for a puzzle with long lasting enjoyment"