Motorcycle Exhaust Install Question?

I just purchased a FMF Q2 exhaust for my 97 KLX300r motorcycle. The description indicated that it bolts onto the stock head pipe. My bike does not have the original gasket for the head pipe and exhaust. When the Q2 was bolted onto the frame it did not completly cover the stock pipe. There are three horizontal slits that are not completely covered which will cause the pipes to leak before the exhaust. I purchased an exhaust repair kit which consisted of a high temp fiber material that is clamped down on the slits which seals them.Question is will this suffice in keeping the exhaust flowing without leaking or will it pose a problem down the line? There doesn't seem to be any leaks when I started the bike. Should I use some silicone sealant as well? Please help!I am trying to install a sliencer/Spark Arrestor. I have stock pipes that I am having problems bolting the silencer onto.

are you trying to install an exhaust pipe or asilencer.