[Effduration]

Sorry to hear... Looks like a pretty thorough and expensive rebuild - time, effort and money... I can fully appreciate how deflating an oil leak like this is after such a rebuild.

I can't see the video but the description of a steady drip to me indicates that the leak is coming from somewhere under pressure. Unless there is a crack in head or or block near a pressurized gallery, this would rule out just about everything except the gallery plug.. The gallery plug is also exactly at the point on the metal shim. above the starter. But the plug, based on photos and your description, looks like it is installed correctly.

I would pour a bottle of oil-compatible UV dye into the oil fill and run it again with transmission off to identify your leak. Then use UV glasses and a flashlight to see it.

 

[Effduration]

Mounting the starter without the transmission installed on an M54 is a challenge.

Does your old Auto transmission have a removable bell housing? Some do, Some don't
I actually have just a bell-housing for the M54 test stand I hope to build some day.

Otherwise, maybe somebody can fab up a chunk of metal using the thin metal shim piece between engine and trans as a template. I don't think the shim itself with a couple of sockets and bolts will be strong enough.

 

[Effduration]

Yeah I think you should just run it with your slick Starter adapter....

If it drips again like it did before, you should be able to see the source...

I don't have a perfect answer on running the engine without a load...But I have re-ringed several M54's and I don't think you're going to cause any damage by running without the trans attached and/or under load...

 

[Effduration]

Did you see this thread?

Massive oil leak after rebuild (solved: oil gallery plug)

I treat it as a pipe plug. My hands tell me when it's enough. Sealant does the rest.

www.e46fanatics.com

Cleaning the threads in block of all oil and the use of a good sealant seems critical.
MrMCar recommended Permatex Form-a-seal #2...non-hardening sealant.

 

[Effduration]

Ladies and gentlemen, we have a winner! Regular blue Loctite 243 looks to have done the trick. Ran the car for about a minute, no drips. Took the flywheel off and everything looks bone dry. Previously, it would start to pour out within seconds. Finally! Might actually take it for a drive this weekend.
Thanks team!

Good stuff...Did you fully seat the gallery plug, or did you leave it flush(ish) to the surface?