Using a dye light is an option, but i'd like to first check some more options.
Using powder sounds good - worth the try.
Any other ideas?
new motor painted with fresh oil and a relatively slow leak and at this point you can't confirm where it is coming from.....well you can start throwing new gaskets at it....or get a dye kit as it will VERY clearly show you source.
flour is old school and works "if" you can get the flour on the core source of leak and if so actually see the discolored flour
at this point you and the rest of us are just guessing as to where the more common leak sources are
pour the dye in, drive for about 15 min, pull car in garage and let cool. Best to check in darker environment and you should get the car up on jackstands as you will likely discover the leak source from under the car. It will lite up like neon green when you see oil. Follow the trail
There are dye "kits" that have various fluids for different parts of car (AC, oil), pair of yellow lens glasses and a UV flashlight (aka black light). Most auto part stores either have these things sold separate or in kit form. IIRC I got mine at Harbor Freight. Gonna cost WAY less than throwing new gaskets at various places let alone time
Your note about finding oil on/near spark plug base to me screams VC....but IMHO you need, at this point, to use something that will reveal the leak source
Sadly if it is RMS...everything come out of the car