So I'm trying to replace the radiator, but when I went to put it in, I noticed that this piece was bent up. What's the best way to bend it back without damaging anything?

also, should I replace the AC condenser as well?
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Are you talking the lower radiator core support? If it is truly bent, it would be wise to bend it back. Hard for me to tell what is bent in that pic.

 

Agreed, its very hard to tell what is bent in the pic as it looks pretty normal from this angle. The method of straightening would depend on where, how much, and how localized the bend is (IE did it hit a rock that only crinkled a few inches way out of whack or did it hit a parking block that slightly bent the whole thing).

 

They make cleaners for the a/c condenser. If it is still functioning, keep it. Now would be the perfect time to do an actual thorough cleaning as it does look like the air flow is restricted. You Tube it...