that bb sized whole is most likely there to drain moisture out of the muffler that builds up. if the y pipe is leaking check to make sure that the bolts are tight up to the manifolds. the kit from summit would change the sound, and might give u sum better performance, but if the problem is in the y pipe ur just gonna have to get another one.
89 Black Hatch, 306, stock heads upgraded springs, XE274HR, Trackheat w/ 70mm T/B. shorties catted Hpipe, Flows, 4.10s manual V/b AOD w/ 3800 stall. 100 Shot. Best Time 1.60 7.55 @ 90 11.89 @ 113