"Seems" doesn't necessarily mean much. Solder it back (just don't keep the soldering iron in contact for long; just as quickly as possible for the solder to connect, but not long enough for the capacitor to melt).
IF that fails, or the omni pattern still doesn't work, THEN the value of that capacitor begins to have a meaning.
I mean, if it's already f**ked... What do you have to lose?
If your car happens to lose a nut from one of the wheels, does that mean you need to change the wheel?
Although looking at NT1a schematic, size and reading about some other people's issues i have a feeling that cap should be 100nf. Could be mine is faulty/weakened as well. It shouldn't make a world of difference, but maybe try 100nf if 20nf doesn't work our for you. Also make sure you clean up the area well after soldering, no residue flux allowed here!