Can someone tell me what I need to fix this ruptured seal? Do I need to replace the whole drag link? How bad is it to drive it like this?

For some reason I cannot find a part number for the seal, I have been searching all day.

 

Your local Carquest/Advance, Napa etc. should have a "Motoromite" section, which should have replacement TRE boots. Otherwise, ask your counterperson for a replacement tie rod end boot.

 

Is it hard to replace? Will I need an alignment after replacing the seal/boot (due to removing the bolt and re-installing it?).

 

Depends on how hard it is to get the end our of the knuckle. Once it's out should just be able to pop the old one off. Once it's off pump new grease in until the grease coming out looks good. Wipe excess out and install new boot. No alignment needed if you don't move the tire any.