Hi and welcome!
The problem can still be the pimple but it is mostly the surface of the main lever that is too smooth from wear.
In the library above you will find the 1019 service manual and in the blow up on this page:
you will see that the main lever (item 191) and the pimple (item 208).
The main lever surface that touches the pimple is sandblasted-rough when new. This roughness wears smooth from the pimple over the years an must be re"roughened". This can be done with some mid-grade (100/120 grit) sandpaper which must be applied in a few sharp strokes to the main lever, perpendicular to pimple movement.
This will leave some mild tracks for the pimple to grab on to. The pimple if worn too much, can be replaced by the one sold by Revisound:https://www.ebay.de/itm/Steuerpimpel-fu ... Swol5YzBvK
Once the main lever is roughened and the new pimple(or useful old one) is re installed, it is vital to smear a very thin layer of grease on that contact surface to avoid wearing the pimple.
I know it sounds implausible to put grease on the area that should have friction, but that is what the sand blasting/sanding does- provide friction. The grease film protects the pimple from premature wear because every time the changer is engaged (Start) the very first movement of the main lever is a full drag over the motionless main lever.
You may also want to look at the full restoration of the 1019 and other Dual on my webpage under service tips, available via the "blue ball/Earth symbol" to the left.