Column or floor shift? Either way it makes sense to work from outside in - start with checking the linkage for play and bad bushings, bleed clutch hydraulics too. Porous clutch hydraulic lines and/or worn out slave cyl produce the same symptoms you've described. Would be surprised to learn the engine had been rebuilt but the clutch not touched. And sometimes fresh tranny fluid alone immensely improves shifting performance. In fact what you're describing sounds alot like 80-90 wt gear oil in the tranny. Oughta be red Type F ford ATF never 80wt gear oil.

An excellent rescue, the 220D 4-spd. Nothing you do to improve the car will be a waste of time, big ticket item the 114/115 sedans.