Grease is the word!
Curt, I suggest you take the clutch cable completely out of the bike,
then fashion a funnel out of stiff plastic, held with a zap-strap, at the
top of the cable, then fill the funnel with oil. Work the cable up and
down a few dozen times, and the oil will gradually run into the cable.
While the mechanism is apart, you can grease everything.
I am guessing you will find some gizmo is jammed with congealed
old grease, and the clutch will work smoothly when you are done.
If the pull remains stiff, then I change my guess: perhaps the
previous owner put in a Barnett clutch, with its stiff springs.
I am very busy getting ready for the northern trek.
So I will look forward to seeing your Benly in a couple of months.
I have loaded and unloaded my Wee-Strom onto my trailer ten times,
and I am not going to do it again. I'll ride my little bikes in Canada.