can't put in gear 1985 bmw 325e

today,upon starting to leave,i couldn't get my 1985 bmw 325e into reverse,i couldn't get any gears at first but after aprox. 7 or 8 min.'s i was able to get 3rd gear which i managed to take off in.after going several miles the gears started taking a little easier.afterparking a couple of hours,same routine.there was a slight grinding a couple of times upon changing from 2nd to 3rd also clunked a few times as was forcing to change.can you please help me with a diagnoses on this?