91 Coupe Quattro Exhaust Manifold Cracked

[PrschRS911 at aol.com]

I think this problem was more common on the 5000 series, and have only seen a
couple of mentions of it on the 20V Quattro list, is this not a common
occurrence on the Coupe Quattros or 20V's and I just got lucky (unlucky)?  I
am replacing the clutch and so while I am at it I thought I would pull the
exhaust manifold and replace the gaskets as I could see evidence of a small
carbon leak from the gasket on the rearmost cylinder.  I could also hear a
slight leak, especially now the car is lowered and running on lower profile
tires - almost sounded like fuel pinging which I could hear inside the car
(even with the Scorpion exhaust).  It was not that noisy in the engine
compartment, although I could feel some hot exhaust gasses at the rear of the
engine, but not much...

Once the manifold was removed, I could see that the rearmost and frontmost
cylinder gaskets were leaking and partially degraded at 9 o'clock and 3
o'clock respectively.  I assume this means the manifold had warped slightly,
all the gasket degradation appears to be on the manifold surface so I am
confident the head is fine and looked ok against a straightedge.  The car has
never overheated, run low on coolant, etc...  I noticed a hairline crack
about two inches long on the outside of the manifold, and looking closer,
noticed that it is cracked inside as well in a different place between two of
the runner channels.  I ground out the crack on the outside for welding and
brought it to a welding shop today to be TIG'd, and then it will go to the
machine shop to be surface milled flat across the ports.  I plan on using Lab
Metal on the crack inside the runners.  My thought is that once it is welded,
all of the warping it wants to do will have already occurred and it will then
be structurally reinforced and sealed externally.  The Lab Metal will seal
internally between the runners.  I also ordered a replacement right-side
engine mount (from GPR - those guys are helpful), although the original looks
strong and non-fatigued.  Somewhere I read that the cracking may be due to
loading on the exhaust when the mount is fatigued.

What do you all think, does my solution sound reasonable?  What are the
alternatives, are there upgraded or improved exhaust manifolds available?
This is the original cast iron manifold from the factory.  I saw mention of a
different type manifold in a previous listing, but no details or info.  Does
anyone know the whole story on the cracked exhaust manifolds?  Thanks in
advance!  Tim