I know you bought the gasket already, but if you want it return it to try this free alternative?

When I did the body lift on my current T, the instruction on the body lift indicated that I need to drill a new hole for the gasket about a inch lower on the firewall (firewall had to be notched an inch lower). After looking at it, it was easier to just toss it and not have a gasket there. After driving the truck w/o the gasket, you can definitely feel the warm air from the engine (or cold air in the morning), and it's much noisier.

The following week, after studying the hole I created (larger than prior as the shaft sits about an inch lower), I decided to look around the garage and found a foam pad from my kid's BMX bike handlebar(my original thought was to use one of those water noodles for the swimming pool...find at Walmart or toystore...similar material). The foam pad is sturdier (heavier density) than the foam that is used for hot water plumbing, but soft enough to just tug it in through the hole. So I basiclaly just wrap it around the shaft from the inside, and squeeze it in through the hole so 1/2 is on the other side of the firewall. I then tape up the foam on both sides. It seem to work great as it seals the hole, and there is no bind while turning.

I know this is not a permanent fix, but I have not had any issue with this for the past 4 months, and it was cheap, free, and took just a few minutes.