Manifold/Blow-by resolution

[Ando]

Which manifold should I use?

The light blue manifold that says “Universal” came with the engine and I have seen blow-by emanating from its connection to the block.

The cause may not be the manifold itself, but rather because the three bolts were a bit rusted and the nuts weren’t on as securely as they should have been despite a Herculean effort getting it to 35fp using a torque wrench.

It may also be because the manifold gasket had no sealant on either side of it, though I know that the gasket is not supposed to have any sealant on it (it’s supposed to go on dry). But I’m putting sealant on it anyway when it goes back on.

The other manifold that says “MMI” is one I scored awhile back. It looks like it has not been used or only slightly. Side note: why does it have a removable “cap” in the fore? And why is the aft bolt hole oblong in shape?

[Al Schober]

One has a removable plate (MMI) because some A4 installations take the exhaust out the other end of the manifold. The plate allows the MMI manifold to be used for either type of install. No idea why one hole is oblong.
As for which one to use? Well, if you need the exhaust at the flywheel end, the choice is easy. Otherwise, pick the one with the least internal corrosion. One of those 'pencil' cameras that work with a smartphone (cable or wifi) is a fun tool and not too expensive.
The joint between the manifold and the block shouldn't leak. And I don't recommend sealant there. If you feel compelled, just put it on the side of the gasket against the block. Put them together without any gasket and check clearances - something odd going on? Another check would be the length of the studs - perhaps they're too long (skim cut on manifold?). Some washers should help if that's the issue.