So many repairs... Advice on Exhaust Headers
 

So I bought an ebay exhaust two years ago. Its done pretty well considering, however Ive noticed some issues with the header and front pipe. they dont seem too bad but I'm wondering if I could do better. Im not gonna pay 300 for dc header and pipe on this car. But I noticed when I redid the gaskets that the exhaust holes on the engine head and gasket are a larger diameter than on the header. Not too much but still maybe half a centimeter smaller on the header. Is that a design flaw or is it meant to be smaller?

I'm looking to buy a $200 megan header to try to get a little more power out of my car. Is it worth it? Or am I gonna see the same thing?

The header and front pipe are pretty solid. Theyre not cracked or anything.