The BB on my 1987 Fuji TT bike feels a little crunchy when I get out of the saddle and mash.

Is this a BB problem? Should I ride it until it fails or change it out?

How hard is it to change out the cartridge?

It is a 68 with a square spindel. I don't know the length. What should I use as a replacement?

Thanks as always.

RFC