I've won a few of those myself and competed in 2 world championships. I'll stick to oil.
It's not law, use what you want. Just answering an implied question for those that are new.
The modern synthetic grease is by far superior to the 19th century lubes the originals used. I try to give my customers the best technology available to me which is why coils are used along with synthetic lubes. Folks tend to like revolvers that don't need frequent repairs and won't wear out.
It's like having a classic automobile that won't be worn-out by 100,000 miles.
Mike