Update, found the right sling shot not working - cause broken armature. No spares so will replace.

Also it wasn't the 3 drop targets setting off the left sling shot, but the Oblong Stand up target (part 31on the upper playfield parts list), directly behind the 3 drop targets. When hit by the ball the left sling shot fires. Maybe this is normal  - not sure

Will fix the right sling shot and see if that makes any difference (have my doubts!)

Thanks MartyJ, got to go to work so will try your idea later. Cheers