HI Scotty,

I'm going to replace my cat this weekend. I have done it many times with aftermarket cats, but none of them lasted long. The OEM part from dealer is so expensive ($5000 CAD including parts and labor). I bought all gaskets and nuts from dealer. I'm wondering what kind of sealer paste I can use to apply on the gaskets to prevent future exhaust leak. In my previous installation, I didn't apply any sealer, it was leaking.

Vehicle info:
Make: Subaru (2009)
Model: Forester
ODO: 230K KM ~ 143K miles
Engine: None-turbo 2.5L
Cat: Front menifold
4 gaskets to be replaced:
1. 44011AC030  Qty: 2 (between engine block and the manifold)
2. 44022AA123  Qty: 1 (between 2nd cat and resonator) 
3. 44616AA030  Qty: 1 (between the manifold and 2nd cat)

The reason why I have to replace gasket 2 (donut gasket): I can't install the manifold properly if I don't take out the 2nd cat.

Your recommendation would be appreciated.