8th edition Concise Oxford Dictionary shows spoilt/spoiled as
interchangeable, however lists spoilt as an entry of it's (grin) own.
1983 Chambers 20th Century Dictionary shows spoilt as a past participle and
past tense only to be used in the sense of damage.
Websters Online dictionary has very similar entries for both, spoiled first
appearing in popular literature in 1385,
spoilt in 1596.

If MT used spoiled, that is my bad.

I was only replying to a slightly frivolous message from Dr. Bush in
(hopefully) in kind.

Words truly can be monsters.