Steve, I don't know what screw pitch your 'turns' are following and I see no pictures. But I think you know how I set mine up. These issues you are having are strange to me as I have not had a failure. I set my intake manifold once and done, which is no different than the factory.
I guess everyone has their own way. To impart my methods only serves to upset others so I've learned to, 'say it once and let it go.'
I do extensive Oil Modifications to my FEs and I document them
. Also notice that I chase all the threads in my castings. I make sure all threads are clear & smooth and they go full depth. I sink a magnet then I wash the holes out using high pressure.
Most shops won't be as meticulous or demanding because time is money. - Dave