My original plan had been to link the servo to the syringe and actuator using a piece of wire. This is how I understand is the standard way. However I tried various pieces of wire and techniques to get the wires the correct length and stay in place. Nothing really seemed to work reliably enough.
I guess I got a bit fixated on using a wire as the con-rod. As a quick test I just modeled something up and printed it. This new printed con-rod works perfectly.
On another note the tip of a toy day that I planned to use as the suction cup proved to unreliable. So I spent an evening looking for some commertial suppliers. I did find one company who offered 'no order too small'. A few emails later they were kind enough to send me one for free.
The difference between this and the toy is light years apart. From a few inial tests a syringe providing the vacuum is able to hold a piece for close to a minute.