I had a new cat welded onto my car recently. I've been back to the guy a series of 3 times because it was leaking a little around the welds. Well I finally got back the 3rd time, and its leaking again! Except is only a very little leak on the outlet of the cat. I can only feel a little air coming out. Is this a big deal? Its just such a hassel to keep going back if this tiny leak doesn't really matter

 

It's a big deal because when you pay someone you expect them to do it right, especially when they had the chance to fix it a couple of times.

The leak in that spot won't affect you much as far as performance goes, but it will make some noise and it will probably develop into a larger leak. I'd say take it back or take it to someone who knows how to weld.

 

3 times and it still leaks? I'd take it somewhere else and have it done right. Afterwards, I might even take the bill over to the original guy and have him compensate me for the 2nd shop's work.

As MadWolf pointed out, you won't experience any performance loss due to the leak; but if the guy can't weld, I guarantee the leak will grow over time.

Thomas.