I never check the other forum, so it was probably a good idea to double post. {not for any info I may give, but from the smart guys....}
My W123 240D often gets kinda hung shifting between 2nd and 3rd. Happens very seldom, but it is a good hang up. I really have to ram it out of where it gets stuck. I don't know about your set up, but my '80 240D had collars that connect the shifter rods to the tranny shafts. Mine were loose when I first got the car, and I could never get it past 2nd gear. I tightened the collars on the shafts from tranny, and I could move through all gears. I suspect mine are either loose, or just not lined up squarely.
It may be worth checking on yours to see if you have the same type of set up, and if so, maybe you have an inexpensive fix. Let's hope......
