Hi Alex,

I put a stainless exhaust manifold in my 850 which had a broken flex section with no issues.
Purchased on Ebay, It was made in EU, Latvia or Poland?

Later I found out that one of the local Boston Muffler shops were welding aces,
and they could have welded in a new flex link and saved a lot of hassle.

If you do install the stainless exhaust you might order a set of titanium exhaust flange studs. I found mine at Ebay, Race Ti, UK (www.raceTi.com) less than $20 shipped.

I don't know if aluminum exhaust manifolds can be welded, but it wouldn't hurt to inquire.

If you can see the crack, plan B might be to try High Temp JB-weld which is designed to repair high temp cracks.

https://knowhow.napaonline.com/how-to-use-jb-weld-extremeheat/

This is worth a look, and easily wind up being Plan A?

Good luck, Bill