The fit could have been due to worn pars (which you'll never see on the outside) or the arc's have been modified to fit the owner so they don't work for you.
Now for something different, I need some input. I have a SRD-7 Pro PCB all drawn up but I'd like to know if you thought it was a good idea to place jumper's on the PCB for the signal coming out of the transformers. All the input wiring is there but I'm not sure if Stax passed the output though the PCB too on the older models. A pic but it is much smaller then this to say the least, roughly 4*2.3".