454 tbi manifold options

[Circuit Rider]

Hey guys, I have been lurking around, looking for answers to no avail. Here is the dilemma, both exhaust manifolds on the 87 454 tbi motor with AIR holes are cracked and leaking. With the oxygen sensor located on the left side manifold I feel that it is telling the computer to go lean so it is increasing the fuel causing the motor to run extremely rich. Does that sound about right?

Here is my next question: what is the best brand of manifold to purchase as far as fitment? Advance auto sells a Dorman brand but is there any other brand that would be any better or should I look for stock used replacements. Please let me know and help me out on this issue as I need to purchase soon. Thanks