For some reason this version has tank problems. I have owned a 360, 450, (2) 550's, (2) 650 supers, and (2) 750's, and my 450 has the same problem as yours. None of the other saws have ever had a tank problem. I bought a used tank for like $39 from chainsawr.com and I am just about ready to put it in.
Anyways, be careful, as the problem might not be the gaskets.
Also, look for a 550 carb to put in your saw. The 450's came with a fixed H jet and it sucks. The 550 carb has an adjustable H jet and is fully compatible with the 450. I already did this mod on my saw, right before I realized the tank was shot. I was wondering why the saw was smoking so much.... lol. Running on like a 1:1 mix of gas and bar oil.