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I have a relentless oil leak at the T-fitting on My Aerovee turbo... it's at the top right of the engine (looking forward), non-turbo Aerovee just have the oil sensor screwed into the engine block there I think. This is the T-fitting that attaches to the oil sender and also sends oil to the turbo.

I have tried everything I can think of for this very small but relentless leak.. I've tried tapping deeper for more thread engagement, I've tried EZ turn fuel lube, two types of PTFE thread sealant, Aviation Form-A-Gasket on the threads, but this continues to be my weak point for pressurized oil leakage. I don't want to over-tighten the T-fitting for fear of cracking the case, which is also tricky considering I have to point the T in only one direction (facing the back of the engine for the turbo oil line.) I've also confirmed that the leak is coming from the T-fitting to Engine block threads and not the other taps into the T-fitting.

I'm at the point where I think I want to try a new fitting, currently using the Brass T-fitting supplied in the kit. Might try a new brass fitting, maybe a steel one, maybe an aluminum one? Any issues with different metal types on the magnesium case?

I'm wide open to suggestions on how to get a good snug thread seal here. AFAIK this is the only tap that goes directly into the case and I want to avoid at all costs the chance of cracking the case.

P.S. I think part of the problem at this fitting is the fact that the (relatively heavy) oil sender is hanging off the end, so my leak may partially be a result of engine vibration.

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I would suggest an AN fitting to the hardline, and then you can use a Y an fitting outside the plenum/airbox to feed the turbo and a separate line to feed the oil pressure sender which can be mounted to the back of the plenum or even the back of the firewall or the engine mount or some other location of your choosing where you don't have that mass flexing the fitting. Lots of solutions to that problem if you really think its the mass of the oil pressure sender, In any case I agree that having the sender as a lever absorbing all that vibration is not a good solution.

Most of the brass fitting available these days are made in China. They aren't any better at cutting threads than they are at making plastic products.
Get a "real" fitting and try that.

Option 2 would be to remove one of several oil galley expansion plugs and tap that opening for the turbo line. Not recommended on an assembled engine though. Too big of a chance getting shavings in the system.
P.S. You might already have a tapped hole where the oil restrictor would have been. The only problem with that is the size of the hole. It's only 1/16 pipe thread. I had a hard time finding a plug when I modified my aluminum case, much less a suitable fitting for an oil pressure fitting. in any case, stay away from Home Depot brass fittings.