Definetly get the shifter gasket!
That damn shifter gasket lol.........I had them on all three of my cars (bought three sets from the guy at the same time because of the reviews) and not only were they a pain in the ass to line up with the bolt holes but they had ridiculous overhang over the edge of the transmission mounting surface. After installing/uninstalling the shifter a couple of times, something happened with the through-holes so that they broke open and then the gasket just fell completely apart in my '95 Cobra. It literally came apart in pieces-----I went back to the RTV gasket stuff.
It not that the shifter has that much flex. If you really shift HARD it can be forced too far and damage the shift forks. The adjustable stops prevent this from happening. The t-45 does not have internal shift stops. I don't think you would ever notice it going too far under regular/semi spirited driving though. Thats my understanding anyway.