So upon removing my Lim and noticed that my rear lower inner Runner has a crack in it but on the other side of it seems okay is this a concern should I just weld it up or leave it be ?

 

That's probably just casting flash or a casting artifact. I seriously doubt it would crack all the way through.

If there is other signs of damage like the manifold was hit hard or something out of the ordinary it might be worth doing something, but that just looks like an irregularity in the casting.

I've NEVER heard of anyone having problems with a manifold breaking or cracking.

Dale

 

I agree its probably a casting flaw. I see it pretty often.