Have you checked also if the hammer will fit into the powertube without use high Forces ??? The hammer should dive in the powertube may 1/2 Inch and not just hit the top of the tube !!!
The seal you changed normaly never get damaged, an example: in my Model98 it´s still the first one and she is over 17years old.
Get a stock powertube and i´m pretty shure if you have assembled everything right she will run !!!
How noob you are ??? Shure a metal powertube got a longer lifetime but the stock one isn´t that bad and your hammer will fit 100%, i´ve changed at my A5 may 3 times cause it broke but the last one is now ca. 5years in use without any Problem !