[Jayce]

First off, did you replace the selenium rectifier with the correct diode and resistor combination? (Can't think of them off the top of my head, so someone help me here.) The 19T8 is then the next candidate due to all the jobs it handles. If audio is bad on AM and FM, that could be at least part of the cause. Also, recheck your 35C5 while you are at it or even try another good 35C5 or even 50C5 as those can be swapped. The alignment issue with FM seems to be common. My Zeniths are not as bad as yours, but still a little off. All these old AM-FM radios need a proper FM alignment, but I don't have the equipment and have never known anyone with the equipment to do so. AM usually just needs a signal generator and the correct instructions and perhaps some special tools. FM also needs an oscilloscope.
I do agree with the attitude towards the 19T8. They can go bad without warning, even if NOS. I have had two do that to me. One was used, lasted a week, then went to a short on one section. A NOS Sylvania tested great, worked for three days and went to a dead short!
Of course, always check the 12AT7 and 6AB4 as those tubes can be weak due to not being used on FM much. The filaments stay on when switched to AM, but the plates get shut off, which is actually hard on any tube.