Exhaust leak on wastegate hurting performance

[nuclearxp]

After I reinstalled my new turbo, I was unwise and didn't use new gaskets on the downpipe connection to my wastegate. The wastegate is a 4-bolt internal unit on a T3/T4 hybrid. The downpipe flange on the exhaust is the 2-bolt style. The leak is just enough at idle to spit out condensation when the car is really cold, but I'm unsure how much it's leaking under load. The car bucks and shudders pretty good under any sort of throttle while cruising. I've recently gone to a fresh base tune. I unplugged my MAF, reset my fuel trims, and started trying to cruise around to narrow down my VE table and fuel trims. The basic trend is that the fuel trims have been highly positive (15-25). I tried adding to the VE table and reflashing but the car is still running real lean. My wideband (which is downstream of the leak) is reading 16-16.5 under light cruise load. I didn't think a small exhaust leak could really be so detrimental after the turbo, but could it be throwing my fueling off that bad? Thanks for any advice, and I can provide scans if it helps.

Pic: This is of the OLD turbo, but the leak is coming from the bottom side, between the up/downpipes.

Edit: Something else I noticed. The wastegate I used for my old stock style turbo covered the exhaust turbine opening just fine. Since I upgraded to a 52 exhaust turbine, the clearance between the outside of the turbine outlet and where the wastegate meets up to the turbo is extremely small. I don't think it's leaking there, but are there any tricks to covering this gap better? Do they make different 4 bolt internal wastegates made to accomodate a larger exhaust turbine?

 

[nuclearxp]

Update: After looking into it some, I guess the concensus is that exhaust leaks after the turbo don't hurt performance. I'm starting to lean towards a vacuum leak now. Vacuum at idle is only around 7 psi, which I've heard is low. I've tried the carb cleaner method for finding a leak but came up empty handed. Any ideas?

 

[turbo nasty]

7 " is a bit low. Check the vac block on top off the TB, EGR and all the IC hose connections.
I had no luck with propane, brake clean, carb cleaner, etc and the only way I found mine was a psi test through the compressor inlet

 

[nuclearxp]

I've pulled the vac line off the top of the TB that goes to various stuff and taped it off, didn't seem to have much impact. I sprayed around the EGR and didn't notice much, and it's really tightened down good on there. What do you mean by a psi test through the compressor inlet? You mean take a compressor attachment and pressurize the whole area and listen for leaks coming out?